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Gilbert Mineralogy - Part II

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PART III.

DESCRIPTION OF MINERALS AND MEANS OF IDENTIFICATION

The more important common minerals are classified into two groups according as they have large economic importance as ores or are useful in the arts or are important as rock forming minerals. Let us now examine a few of these minerals and see if we cannot learn a little more about them.


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MINERALS OF ECONOMIC IMPORTANCE
(Minerals with Metallic Luster)
A.   GALENA

Taken from the Greek galene, meaning tranquility. It was supposed to have certain soothing medicinal properties. It is often called blue ore or blue lead by miners. Sometimes called galenite.

Composition - Sulphide of lead, PbS. Sulphur = 13.4 per cent, lead = 86.6 per cent. Often carries small amounts of silver sulphide and is sometimes valuable as a silver ore. When it contains enough silver to be worth extracting it is called ďargentiferous galena." Whether galena contains silver or not can be told only by chemical analysis. Galena also contains at times small traces of zinc, cadmium, antimony, iron. copper, bismuth, selenium and gold.

cubic crystal

Crystal System - Common form is the cube. (Fig. 21).

Structure - Occurs commonly crystallized or massive cleavable; also occurs coarse or fine grained.

Physical Properties

Cleavage - Cubic and perfect, specimens breaking into small cubes, when rubbed or struck.
Hardness - 2.5 to 2.75. Can be scratched easily by a cent.
Luster - Bright metallic.
Color - Lead gray.
Streak - Lead gray.

Experiment 1. How to Test for Galena - Powder some of the mineral by breaking it up in a small cloth bag by means of a hammer. Now mix a small amount of the powdered mineral with an equal amount of sodium carbonate and heat the mixture on charcoal in the reducing flame of the blowpipe. Notice that a metallic globule of lead is formed, which is bright lead color when hot but covered with a dull oxide coating when cold. Notice that a coating of lead oxide is also formed, which is yellow near the globule and white farther away. Remove the lead globule and notice that it is malleable and can be hammered out into a thin sheet.

Place a little of the powdered mineral in an open tube and heat slowly over a gas flame if such is handy. Do you recognize the odor of burning sulphur? Nearly all sulphides when heated this way or when roasted on charcoal in the oxidizing flame give this same characteristic pungent odor of sulphur dioxide.

Galena is recognized chiefly by its cubic cleavage, high specific gravity or weight, softness and black streak.


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Occurrence - A common metallic sulphide and found associated with such minerals as pyrite, chalcopyrite, sphalerite, anglesite, cerussite, quartz, dolomite, calcite, barite and fluorite. Also found with silver minerals and sometimes contains silver in sufficient quantity to make it an important silver ore.

It is found in Missouri occurring in the form of beds. disseminated through limestone and also associated with zinc ores. It is found as lead-silver deposits in Idaho, Utah and Colorado. Important deposits are also found in Germany and England.

Uses - It is the most important lead ore and an important ore of silver. Metallic lead finds many important uses, some of which are as follows: as sheets and pipes; in making shot, bullets and weights, in some alloys as solder (tin and lead) type metal (antimony and lead) and low fusing alloys (bismuth, tin and lead) commonly called Wood's metal; large amounts are used in the form of basic lead carbonate, commonly known as white lead, in paint making; in the form of  litharge (PbO) and red lead (Pb3O4) for making fine grades of glass, for glazing earthenware and as pigments; in the form of lead chromates for making red and yellow paints; in many industries in the form of lead acetate (sugar of lead). Galena is also used as a detector in wireless sets.

B.   STIBNITE

Sometimes called gray antimony, antimony glance or antimonite.


Composition - Antimony trisulphide, Sb2S3 Antimony = 71.4 per cent, sulphur = 28.6 per cent. Occasionally contains silver and gold.

stibnite crystal

Crystal System - Usually in the form of elongated prisms vertically striated. Crystals sometimes bent or curved and steeply terminated. (Fig. 22.)


Structure - In radiating crystal groups or in bladed forms with prominent cleavage. Sometimes massive, coarse to fine granular.

Physical Properties

Cleavage - Perfect.
Hardness - 2. Can be scratched with the finger nail.
Specific Gravity - 4.5 to 4.6. Fairly heavy.
Luster - Metallic, splendent on fresh surface.
Color - Lead gray.
Streak - Lead gray.

Experiment 2. How to Test for Stibnite - Heat a small piece of the mineral in a gas or candle flame and notice that it fuses or melts very easily.

Heat a small amount of the mineral on charcoal in the oxidizing flame of the blowpipe and notice that a heavy white coating of antimony oxide is formed a short distance from the mineral and the burning mineral gives the irritating odor of burning sulphur.



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Heat a little of the powdered mineral in an open tube and notice that two sublimates are formed, one a white non-volatile sublimate on the bottom of the tube and the other a white volatile sublimate in the form of a ring around the tube. Heat a little of the powdered mineral in a closed tube and notice that the mineral gives a faint ring of sulphur and a red deposit of antimony oxysulphide when cold.

Stibnite is usually recognized by its bladed structure, perfect cleavage, soft black streak and lead-gray color.

Occurrence - Found usually in beds or veins of quartz, granite and gneiss. It occurs associated with other antimony ores and with calcite, barite, galena, cinnabar, sphalerite and occasionally gold. Found in China, Japan, Mexico, New South Wales, Saxony, Bohemia and in small deposits in California, Nevada and Idaho.

Uses - Metallic antimony is used in several alloys such as type metal (antimony, bismuth and lead), britannia metal (antimony and tin), babbitt or anti friction metal (antimony, tin and lead) and pewter (antimony and lead). Antimony sulphide is used in fireworks, in safety matches, percussion caps and in the vulcanization of rubber. Antimony trioxide is used as a pigment and in the glazing of enameled ware. Other compounds of antimony like tartar emetic are used in medicine.

C. CHALCOPYRITE

Sometimes called copper pyrites and yellow copper ore. Derived from the Greek word meaning brass. 

Composition - Sulphide of copper and iron, CuFeS2. Sulphur = 35 per cent, copper = 34.5 per cent, iron = 30.5 per cent.


sphenoids
Crystal System - Usually1ly wedged shaped in the form of sphenoids. (Fig. 23.)

Structure - Occasionally in crystals, but more often massive and compact.

Physical Properties

Fracture - Uneven, conchoidal.
Hardness - About 3.5. Can be scratched with a knife.
Specific Gravity - 4.1 to 4.3. Fairly heavy.
Luster - Metallic and opaque.
Color - Brass yellow, often tarnished to bronze.
Streak - Greenish-black and slightly shining.

Experiment 3 - How to Test for Chalcopyrite
- Powder a little of the mineral and heat a small amount mixed with a little sodium carbonate and a little borax on charcoal in the reducing flame of the blowpipe. Notice the smell of burning sulphur and the formation of metallic globules of copper. Remove the globule from the charcoal and notice that it is somewhat magnetic, for

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it is attracted by the magnet. Also notice that the globule has the characteristic red copper color and is malleable, for it can be hammered out into a thin sheet.

Heat a small amount of powdered mineral in an open tube and notice the odor of burning sulphur. Heat a little of the powdered mineral in a closed tube and notice the separation of sulphur.

Chalcopyrite is usually recognized by its brass-yellow color. softness and greenish-black streak. It is distinguished from iron pyrites in that it crumbles when cut with a knife  while iron pyrites is [sic] not affected by the knife blade. Copper pyrites does [sic] not give off any sparks when struck with steel while iron pyrites does [sic]. It is distinguished from gold in that it is brittle and non-malleable, gold being malleable and soft and easily cut by a knife.

Occurrence - Most common ore of copper. Found widely distributed in metallic veins and associated with such minerals as pyrite, chalcocite, malachite, azurite, sphalerite, galena, quartz, calcite, etc. Sometimes carries gold and silver, in which case it is mined for these metals.

Found widely associated with other copper minerals in the United States, as  in Montana, Utah, Colorado, California and Arizona.  Also found in England, Spain, Sweden, Canada. Mexico, Alaska, Chili, etc.

Uses - Most important copper ore. Copper has many varied and important uses as follows: in wire, sheet and nails; in various alloys as brass (copper and zinc), German silver (copper, zinc and nickel), bronze (copper, tin and zinc), gold coin, silver coin, and nickel coin. Copper sulphate, commonly known as blue vitriol, is used in calico printing and in galvanic cells.

D.   PYRITE

Commonly. called iron pyrites. Name derived from Greek word meaning fire, probably because of the fact that the mineral gives off sparks when struck with steel.

Composition - Iron disulphide, FeS2 Iron 46.6 per cent, sulphur 53.4 per cent. Contains occasionally small amounts of copper, nickel and cobalt.  Sometimes carries small amounts of gold and is then called auriferous pyrite.

striated
Crystal System - Common crystal forms are the cube  with striated faces (Fig. 24) and pyritohedron (Fig. 25).
pyritohedron
Structure - Commonly found in in crystals. Also found massive, granular, stalactitic, globular and reniform.

Physical Properties


Hardness - 6 to 6.5. Rather hard, also brittle.
Specific Gravity - 4.95 to 5.1. Fairly heavy.


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Luster - Metallic, splendent, opaque.
Color - Pale brass yellow to bronze yellow, due to tarnish.
Streak - Greenish or brownish-black.

Experiment 4. How to Test for Pyrite - Heat a small fragment of the mineral, held in the forceps in the reducing flame of the blowpipe and notice that the mineral fuses  When the fragment has become cold, test it with the magnet. Notice that the fragment is magnetic and is attracted by the magnet.

Break a little of the mineral up into the form of a powder and heat a little of the powder in a closed tube, Notice the formation of a large amount of sulphur in the tube. Heat a little of the powder in an open tube. Do you recognize the odor of burning sulphur? This same odor is obtained when a little of the powdered mineral is heated on charcoal in the oxidizing flame.

Make a loop on one end of nickel-steel wire by bending it around the sharpened end of a lead pencil. Heat the loop in the oxidizing flame of the blowpipe for several moments. Then dip the loop into borax and again heat carefully in the blowpipe or gas flame. Notice that the borax puffs up and soon melts. On cooling, you should have a thin, clear transparent bead.  Now place a bit of the powdered mineral about the size of a pin head on the bead and heat the bead for several minutes in the reducing flame. Notice that the bead on cooling is bottle green in color. If heated in the oxidizing flame. the bead would be yellow on cooling. This is the borax bead test for iron.

Pyrite is usually distinguished from gold in that it is brittle; from chalcopyrite by the fact that it cannot be scratched by a knife and is of paler color.

Occurrence - Pyrite is a very common occurring mineral and is found in many parts oi the world. It occurs commonly as a vein mineral and is found widely as an accessory mineral in several kinds of rocks. It occurs associated with many different minerals. Important deposits of pyrite are found in Virginia, New York, Massachusetts, California, Portugal and Spain.

Uses - Pyrite is frequently mined because of the gold or copper that is found associated with it. It is never mined as an iron ore because of the large amount of sulphur which it contains. It has an important use, however,in the manufacture of sulphuric acid and sulphate of iron or ferrous sulphate (copperas). Sulphuric acid is probably the most important technical acid and finds many uses in the industries, such as manufacture of other mineral acids, preparation of fertilizers and as a dehydrating or drying agent in many chemical reactions. Sulphur dioxide obtained by burning or roasting pyrite finds an important use as a bleaching agent in the preparation of wood pulp in paper making. Ferrous sulphate is used in the manufacture of inks, in dyeing, in preserving wood and as a disinfectant. Pyrite is also used as a detector in wireless sets.

E.   MAGNETITE

Commonly known as magnetic iron ore. The name was probably derived from a  locality in Macedonia called Magnesia or to a shepherd named Magnes who is said to have discovered the mineral by noticing that the nails of his shoe and the ferrule of his staff adhered to the ground over which he walked.


GILBERT MINERALOGY

Composition - Oxide of iron Fe3O4. Iron = 72.4 per cent, oxygen = 27.6 per cent. The ferrous iron is sometimes replaced by small amounts of magnesium or titanium.

octohedron
Crystallization - Usually in the form of octehedrons when crystallized (Fig. 26).
Structure - Frequently found crystallized. Other forms are granular and massive, coarse and fine grained.

Physical Properties

Cleavage - Sometimes develops octahedral parting when pressure is applied to the mineral.
Hardness - 6. Can be scratched by window glass.
Specific Gravity - 5.2. Rather heavy.
Luster - Metallic.
Color - Iron black.
Streak - Black.
Magnetism - Strongly magnetic. The variety known as lodestone is a natural magnet.

Experiment 5. How to Test for Magnetite - Magnetite cannot be fused or melted in the blowpipe flame. Try fusing a small fragment in the reducing flame of the blowpipe.

Break a little of the mineral up into the form of a powder and. make a borax bead test as described under the mineral pyrite. Notice that in the oxidizing flame the bead is yellow, while in the reducing flame the bead is bottle-green.

Try the effect of the magnet on one or two fragments of the mineral and notice that the mineral is readily attracted by the magnet.

Magnetite is recognized chiefly by its strong magnetism. its hardness, black color and black streak.

Occurrence - Common ore of iron. Found in many rocks and in some cases in the form of large ore bodies. Also occurs in beds and sometimes found in the black sands of the seashore. Often associated with such minerals as corudum, mica, diabase, gabbro and peridotite.

Found in large beds in Northern New York State. Also found in Pennsylvania. New Jersey and England. It constitutes the chief iron ore in Norway and Sweden. The variety known as lodestone is found in Siberia, Germany and Arkansas.

Use - 1mportant iron ore.

F.   PYROLUSITE

Named from the Greek word meaning fire and wash, because of its power of removing the colors from green or brown glass.

Composition - Manganese dioxide, MnO2. Sometimes contains a little water.



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Crystal System - Usually takes the crystal form of some other mineral, especially manganite.

Structure - Usually occurs massive or reniform; sometimes with a fibrous and radiating structure.

Physical Properties

Fracture - Splintery, mineral breaking into needles.
Hardness - 2 to 2.5. Soft, often soils the fingers like carbon.
Specific Gravity - 4.75.
Luster - Metallic.
Color - Iron black.
Streak - Iron black.

Experiment 6. How to Test for Pyrolusite - Heat a small piece of the mineral, held in the forceps, in the blowpipe flame and notice that the mineral is infusible and does not melt.

Make a borax bead as described under the tests for the mineral pyrite and heat a small amount of the mineral about the size of a pinhead on the bead in the oxidizing flame of the blow-pipe. Notice after cooling that the bead is colored reddish-violet. If heated this way in the reducing flame, the bead would be colorless.

Repeat the above test, using a sodium carbonate bead in place of the borax bead. The sodium carbonate bead is made similar to the borax bead. Notice that the mineral imparts a bluish green opaque color to this bead when heated in the oxidizing flame.

Place a small amount of the powdered mineral in a closed tube and heat over a hot flame. While heating, insert into the tube a toothpick or match which has a spark on one end. Notice that the spark glows brightly and in some cases takes fire and burns with a flame. This is because the mineral gives off oxygen when heated.

Occurrence - Found in beds or nests as manganese ores enclosed in clays. Also found occurring in veins with quartz and various metallic minerals.

Occurs in Virginia, California, Arkansas, Georgia, Australia, Japan, India, Nova Scotia, etc.

Uses - Most important ore of manganese. Manganese is used chiefly in the form of alloys, the most important being those containing iron and manganese. The alloy known as spiegeleisen contains iron and manganese and is used extensively in the manufacture of steel. Manganese dioxide is used as an oxidizing agent in the manufacture of chlorine, bromine and oxygen; as a decolorizer of glass; as a drier in paints, and in the dry-cell battery. Potassium permanganate is used as a disinfectant. Manganese is also used for coloring glass, pottery and bricks and in calico printing.

Minerals With Non-Metallic Luster

G.   SPHALERITE

Commonly known as zinc blende or black jack. The name blende is German, meaning blind or deluded because it resembles galena. Sphalerite is Greek, meaning treacherous.

GILBERT MINERALOGY
 

Composition - Zinc sulphide, ZnS. Zinc = 67 per cent, sulphur = 33 per cent. Part of the zinc is sometimes replaced by iron and often small amounts of cadmium, manganese, etc.

tetrahedrons

Crystal System -Tetrahedrons are the common form.  (Fig. 27). Also found in the form of cubes. Crystals are often twinned and modified so that is is difficult to determine the forms present.

Structure - Usually massive and compact, coarse to fine  granular but sometimes botryoidal or fibrous.

Physical Properties

Cleavage - Perfect.
Fracture - Conchoidal, brittle.
Hardness - 3.5 to 4. Can be scratched with a knife.
Specific Gravity - 4 to 4.1.
Luster. - Resinous and adamantine. Non-metallic.
Color - White when pure. More often black, brown and yellow. Brown and black color due to the presence of iron.
Streak - White to yellow or brown.

Experiment 7. How to Test for Sphalerite - Heat a small fragment of the mineral in the reducing flame of the blowpipe and notice that the mineral is infusible or nearly so.

Break a little of the mineral up into the form of a powder and heat a small amount of the powder on charcoal in the oxidizing flame of the blowpipe. Then heat in the reducing flame. Notice the odor of burning sulphur and the formation of a coating of zinc oxide which is yellow when hot and white when cold. If this coating is moistened with a drop oi cobalt nitrate solution and heated in the reducing flame, it will turn dark green in color.

Mix a little of the powdered mineral with a little sodium carbonate and charcoal and heat on charcoal in the reducing flame of the blowpipe. Notice the bluish green flame that is produced by the mineral. This is the flame color test for zinc.

Sphalerite is usually recognized by its characteristic resinous luster and perfect cleavage.

Uses - Most important zinc ore. Metallic zinc is used chiefly in making brass (an alloy of copper and zinc), in making galvanized iron, in electric batteries and as sheet zinc. The compound zinc oxide or zinc white is used extensively in making paints. Zinc sulphate is used in medicine and in dyeing.

Zinc chloride is used as a preservative for wood. The metal cadmium is often obtained from sphalerite.

H.   MALACHITE

Commonly called green copper carbonate. Name is derived from the Greek word mallows on account of its green color.

Composition - Basic carbonate of copper (CuOH)2CO3. Copper = 57,4 per cent, water = 8.2 per cent, cupric oxide = 71.9 per cent, carbon dioxide = 19.9 per cent.


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radiating fibrous

Crystal System - Crystals usually found in slender prismatic forms.

Structure - Commonly radiating fibrous with botryroidal or stalactitic surface (Fig. 28). Also found granular or earthy.

Physical Properties

Cleavage - Perfect.
Hardness - 3.5 to 4. Can be scratched by a knife.
Specific Gravity - 3.7 to 4.
Luster - Adamantine to vitreous in crystals, Silky in fibrous varieties. Dull in earthy variety.
Color - Bright green.
Streak - Pale green.

Experiment 8. - How to Test for Malachite - Heat a small fragment of the mineral, held in the forceps, in the blowpipe flame and notice that it fuses or melts, giving an emerald green flame. ∑

Break a small amount of the mineral up into a powder and place a little of the powder in a closed tube. Heat the tube over a hot flame and notice that water is given off which condenses in the form of drops on the sides of the tube. Also notice that the mineral turns black. 

Mix a little of the powdered mineral with a little sodium carbonate and borax and heat the mixture on charcoal in the reducing flame of the blowpipe. Notice the formation of red metallic globules of copper.

Prepare a borax bead as described under the mineral pyrite and heat a little of the powdered mineral about the size of a pinhead on the bead in the blowpipe flame for several minutes. Notice that on cooling the bead is colored green. This is the borax bead test for copper.

Malachite is recognized generally by its green color and radiating fibrous structure.

0ccurrence - Usually occurs in copper veins that are found in limestones. An important and widely distributed ore of copper. Found in the Ural Mountains of Russia. Africa, Chile. Arizona and New Mexico.

Uses - Important copper ore. Used somewhat as ornamental material for vases and veneer for table tops.

J.   CALCITE

Commonly called calc spar or carbonate of lime. Name derived from Latin word calx, meaning lime.

Composition - Calcium carbonate, CaCO3.  Calcium oxide = 56.0 per cent. Carbon dioxide = 44.00 per cent. Calcium sometimes replaced by small amounts magnesium, iron, manganese and zinc.



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calcite # 1

Crystal Systems - Good crystals very common. Figures 29 and 30 illustrate two of the more important types of crystallization. Some crystals are very complex.

calcite # 2

Structure - Found fibrous, stalactitic, coarse to fine granular, compact and earthy.

[Physical Properties]

Cleavage - Perfect.
Hardness - 3. Can be scratched by a cent, easily by a knife.
Specific Gravity - 2.72. Not very heavy.
Luster - Vitreous to earthy.
Color - Usually white or colorless. Sometimes colored gray, red, green, yellow, blue, brown and black. Usually transparent, but opaque when impure.

Experiment 10. How to Test for Calcite - Heat a fragment of the mineral, held in the forceps, in the reducing flame of the blowpipe for several minutes and notice that it does not fuse or melt. Moisten a piece of yellow turmeric paper and touch it to the fragment that has been heated. Notice that the turmeric paper turns brown. This is a test for calcium oxide, which gives an alkaline reaction and is present in calcite. If this fragment is moistened with hydrochloric acid and heated, it gives an orange-red flame which is the flame color test for the metal calcium. Small pieces of the mineral also effervesce or give off the gas carbon dioxide, freely, when dissolved in cold hydrochloric acid.

Occurrence - Calcite is a very common and widely diffused mineral. It occurs in very large masses in many rocks. The common rock materials known as limestones, marbles, chalk, calcerous marls, etc., consist essentially of calcium carbonate.  A large amount of these carbonates has been formed by the gradual deposition of shells and the skeletons of sea animals which consist mainly of calcium carbonate. It is found also as a vein mineral occurring with all sorts of metallic ores.

Calcite in its various forms is found widely distributed in many localities. Some notable deposits occur in England, Iceland, Mexico, Missouri, Michigan, and New York.

Uses - Calcite is used chiefly in the manufacture of lime for mortar and cement. By heating limestone to about 1000 degrees Fahrenheit, carbon dioxide, a gas, is driven off and the limestone is converted into quicklime (CaO). White-


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wash is made by mixing quicklime with water, while mortar is made by mixing it with sand and water. Portland cement is made by mixing lime with silica and alumina.

Chalk is used for whiting, whitewash, crayons and as a fertilizer. Large deposits of it are found in the famous chalk cliffs of Dover, England.

Limestone is used chiefly as a building material. Also as a flux for smelting certain metallic ores. The chief occurrences in the United States are in Indiana, Pennsylvania, Illinois, Ohio, New York, Missouri and Wisconsin.

Marbles are used primarily as ornamental and building material. Important quarries of marble are found in Vermont, New York, Georgia and Tennessee.

Iceland spar is a valuable variety and is used for making optical instruments in the form of the Nicol prism to produce polarized light. Found in Iceland.

K.   FLUORITE

Commonly known as fluor spar and derived from the Latin fluo, meaning to flow, being used as a flux.

Composition - Calcium fluoride CaF2. Fluorine = 48.9 per cent, calcium = 51.1 per cent.

cubic
Crystal System - Common form is the cube. (Fig. 31).

Structure - Crystallized. Also found massive and columnar, coarse to fine granular.

Physical Properties

Cleavage - Perfect octahedral.
Fracture - Conchoidal, brittle.
Hardness - 4. Can be scratched with a knife.
Specific Gravity - 3 to 3.25.
Luster - Vitreous.
Color - Colorless, white, green, blue, purple, yellow, rose and brown.
Streak - White.

Experiment 11. How to Test for Fluorite - Heat a small fragment of the mineral, held in the forceps, in the blowpipe flame and notice that it fuses or melts. Also notice that the mineral colors the flame orange. This is the flame color test for the metal calcium.  Moisten a small piece of turmeric paper with water and place it on the fragment that has been heated. Notice that the yellow turmeric paper turns brown. This is a test for an alkali, the alkali present being calcium oxide (CaO).

Test for fluorine is as follows: break a little of the mineral up into the form of a powder and mix a small amount of the powdered mineral with an equal amount of sodium bisulphate. Place some of this powdered mixture, about 1/2 inch, in a closed tube and heat over a hot flame, preferably a gas flame. Notice that after a short while a white sublimate or deposit of silicon dioxide is formed on the walls of the tube. When the mixture was heated, sodium bisulphate was converted into sodium sulphate and sulphuric acid. The sulphuric acid reacted with the mineral calcium fluoride to form hydro-


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fluoric acid which in turn acts upon the glass and etches it. A secondary reaction then sets in with the formation of a white deposit of silica on the glass tube. This is the test that is usually applied to the element fluorine,

Fluorite is usually recognized by its cubic crystals, octehedral cleavage, vitreous luster, color and by its being scratched with a knife.

Occurrence - Common mineral and widely distributed. Usually found in veins or associated with metallic ores such as tin and lead. Also associated with dolomite, limestone, calcite, gypsum, barite, galena, quartz, cassiterite, sphalerite, topaz, apatite, etc.

Fluorite is found as important deposits in Illinois and Kentucky. Also in England and Saxony.

Uses - The better grade of fluorite is used in the manufacture of opalescent glass. Other grades are used in enameling cooking utensils, as a flux in steel making, in the preparation of hydrofluoric acid and sometimes as ornamental material in the form of vases and dishes. 

L.   HALITE

Commonly called rock salt or common salt.

Composition - Sodium chloride, NaCl. Sodium = 39.4 per cent, chlorine = 60.6 per cent. Often contains impurities such as calcium and magnesium chlorides and calcium sulphate.

halite
Crystal System - Usually in the form of cubes (Fig. 32). Other forms rare.

Structure - Usually in crystals showing cubical cleavage and known as rock salt. Sometimes occurs massive and granular.

Physical Properties

Cleavage - Cubical and perfect.
Fracture - Conchoidal, brittle.
Hardness - 2.5. Can be scratched with a cent.
Specific Gravity - 2.l to 2.6. Rather light.
Luster - Vitreous.
Color - White or colorless and, when impure, yellow, blue, purple or red.
Taste - Salty.
Solubility - Readily soluble in water.

Experiment 12. How to Test for Halite
- Heat a small piece of the mineral,held in the forceps, in the blowpipe flame and notice that the mineral fuses or melts very easily. Also notice that it gives a strong yellow flame. This is a test for the metal sodium. Moisten a small piece of yellow turmeric paper and place it on the mineral after it has been heated. Notice that the yellow turmeric paper turns brown, proving that an alkali is present in the mineral.

Break a little of the mineral up into the form of a powder and try to dissolve a little of the powder in some water in a test tube, Notice that the mineral dissolves readily in water. Taste a little of this solution. Do you recognize the salty taste? If this solution was treated with a solution of silver nitrate you would obtain a white precipitate of silver chloride. This is the test for chlorine in a soluble compound.


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Occurrence
- A common and widely occurring mineral. Occurs extensively in beds of great thickness. Found also in springs, salt seas and in the ocean.

Salt beds were originally formed by the gradual evaporation and drying up of salt water which had been shut out from the sea. These beds have then become covered by other deposits of sediment so that salt beds are found to a depth of two thousand feet below the surface of the ground. These salt beds range from a few feet to a hundred feet in thickness.

Salt is produced in the United States either by mining by means of shafts and galleries or by pumping the salt brine from the salt bed to the surface and evaporating off the water, Many important deposits are found in the United States, especially in New York, Michigan, Ohio, Kansas and Louisiana. Important deposits are found also in Great Britain, Poland, Hungary, Germany and Spain.

Uses - Rock salt is used chiefly for culinary and preservative purposes. Also used in manufacture of sodium carbonate for glass making, soap making and bleaching. Also used in the preparation of sodium compounds and in the extraction of gold by the chlorination process.

IMPORTANT ROCK MAKING MINERALS

Minerals With Non-Metallic Luster

The rock making minerals are in most cases complex silicates of such metals as aluminum, magnesium, calcium, iron, sodium, potassium and hydroxyl (OH). The physical properties of these minerals usually afford sufficient means for their identification.

M.   ORTHOCLASE

Commonly known as potash feldspar. The name orthoclase refers to the right-angled cleavage which the mineral has. Feldspar is taken from the German word feld, meaning field. Orthoclase belongs to a class of rock-making minerals called the feldspars. They are complex silicates of aluminum with sodium, potassium or calcium and sometimes barium. .

Composition - Potassium aluminum silicate, KAlSi3O8. Aluminum oxide = 18.4 per cent, potash = 16.9 per cent and silicon dioxide = 64.7 per cent. Soda sometimes replaces part of the potash.


prismatic
Crystal System - Crysta1s usually prismatic in habit. (Fig. 33)

Structure - Crystals common. Also occurs massive and with granular structure.

Physical Properties

Cleavage - Two kinds, perfect and good.
Fracture - Chonchoidal to uneven and splintery.
Hardness - 6 to 6.5. May be scratched by glass or may scratch glass.


GILBERT MINERALOGY

Specific Gravity - 2.5 to 2.6. Rather light.
Luster - Vitreous.
Color - Colorless, gray, white, flesh-red and gray or greenish gray.
Streak - White.

Experiment 13. How to Test for Orthoclase - Heat a small splinter or fragment of the mineral in the reducing flame of the blowpipe and notice that the mineral does not fuse or melt easily. It melts only on the edges of thin fragments.

If the powdered mineral is mixed with powdered gypsum and heated on platinum or nickel-steel wire, the flame will be colored purple, which is the flame test for the mineral potassium.

Orthoclase is usually recognized by its hardness, color and cleavage.

0ccurrence - A very common rock-forming mineral. It occurs widely distributed in all types of rocks and is found associated with the minerals quartz, albite and muscovite. It is largely a vein mineral and is found in New England and Middle Atlantic States, chiefly in Connecticut, Maine, New York, Maryland and Pennsylvania. Feldspar is quarried in large amounts in some of these localities.

Uses - Orthoclase finds an important use in the manufacture of porcelain. The finely ground mineral is mixed with clay (kaolin) and quartz and, when heated to a high temperature, the feldspar fuses and acts as a cement to bind the material together. Fused feldspar is one of the chief ingredients of the glaze on porcelain.

N.   TALC 

Commonly called steatite or soapstone.

Composition - Si1icate of magnesium, H2Mg3(SiO3)4. Magnesium oxide = 31.7 per cent, silicon dioxide = 63.5 per cent, water = 4.8 per cent.

Structure - Usually massive. with foliated structure. Can be split into thin plates, which are flexible but not elastic when found in this form. Also compact.

Crystal System - Crystals rare.

Physical Properties

Cleavage - Perfect, giving thin plates. Can be cut with a knife.
Hardness - 1. Very soft mineral, will make a mark on paper or cloth.
Specific Gravity - 2.8. Rather light.
Luster - Pearly, feels greasy.
Color - White, apple-green and gray.

Experiment 14. How to Test for Talc - Heat a small piece of the mineral, held in the forceps, in the reducing flame of the blowpipe and notice that it is difficult to fuse or melt the mineral. It fuses to an enamel on the edges only.

If a small piece of the mineral is moistened with a solution of cobalt nitrate and heated in the blowpipe flame the mineral will become pale violet in color.

Talc is usually recognized by its resemblance to mica in structure and cleavage, and by its softness and greasy feel.

Occurrence - Talc is usually found as a mineral formed by the alteration of magnesium silicates such as chrysolite, pyroxene, amphibole, etc.


GILBERT BOY ENGINEERING

Soapstone quarries are found in the United States chiefly in Vermont, Massachusetts, Rhode Island. New York, New Jersey, Pennsylvania, Maryland, North Carolina, Virginia and Georgia.

Uses - Soapstone has many uses.  In the form of slabs it is used extensively for making wash tubs, sinks, table tops, electrical switchboards, furnace linings, hearthstones, etc, The compact variety is used as tailorís chalk, slate pencils, gas burners, etc. Finely divided talc is used in paper making as a filler to give weight, as a lubricant, as toilet powders (talcum powder, in paints, as a heat insulator and in several other things.

O.   APATITE

Name taken from the Greek word apatao, meaning to deceive.

Composition - Phosphate and fluoride of calcium, Ca4(CaF) (PO4)3 or phosphate and chloroide of calcium (Ca4)(CaCl) (PO4)3. The first is called fluor-apatite while the second is called chlor-apatite.


apatite
Crystals System - Crystals usually long prismatic in habit. Sometimes found in short prisms. (Fig. 34).

Structure - Usual1y found in crystalline form. Also found massive, granular to compact.

Physical Properties

Cleavage - Very poor.
Fracture - Conchoidal and uneven, brittle.
Hardness - 5. Can be scratched by a knife, better with glass.
Specific Gravity - 3.15.
Luster - Vitreous to subresinous.
Color - Usually some shade of green or brown. Also white, colorless, blue, violet and gray. Transparent to opaque.
Streak - White.

Experiment 15. How to Test for Apatite - Heat a small fragment of the mineral, held in the forceps, in the reducing flame of the blowpipe for several minutes and notice that it does not fuse or melt easily. Notice the orange colored flame produced by the mineral when heated in this way. This is the flame test for the metal calcium.

The powdered mineral dissolves in concentrated hydrochloric acid and gives a white precipitate of calcium sulphate when a drop or two of sulphuric acid is added.

The mineral is usually recognized by its hardness, color and crystal forms.

Uses - Apatite is used chiefly as a fertilizer on account of the phosphorous which it contains, Transparent varieties are used somewhat as gems.

P.   MUSCOVITE

Also known as muscovy-glass or common mica. The name was derived from the mineral muscovy-glass which was used as a substitute for glass in Russia. Mica is derived from the Latin word micare, meaning to shine.


GILBERT MINERALOGY

Composition - A complex silicate of potassium, aluminum and hydrogen, H2KAl3(SiO4)3.  Frequently contains traces of iron, magnesium, calcium, sodium, lithium, fluorine and titanium.

mica

Crystal System - Usua1ly in the form of six-sided plates (Fig. 35), Also massive and in scales.

Structure - Large and small sheets foliated. Sometimes in scales. Distinct crystals rare.

Physical Properties

Cleavage - Extremely perfect, mineral can be easily separated into thin sheets. Sheets are flexible and elastic.
Hardness - 2 to 2.5. Can be scratched by copper coin.
Specific Gravity -2.76 to 3.
Luster - Vitreous, silky and pearly.
Color - White, yellow, brown, black and green. In thin sheets the mineral is transparent and almost colorless.

Experiment 16. How to Test for Muscovite - Heat a small piece of the mineral, held in the forceps, in the blowpipe flame for several minutes and notice that the mineral does not fuse or melt very readily.

Muscovite is usually recognized by its light color and mica-like structure.

Occurrences - A very common and widely distributed rock-making mineral. It is found in many types of rocks. Muscovite is found in veins associated with quartz, feldspar, tourmaline, beryl, garnet, fluorite and apatite.

Muscovite is found in the United States chiefly in the Appalachian and Rocky Mountain regions. It occurs in pegmatite veins in North Carolina and South Dakota. Deposits are also found in Connecticut, Maine, New Hampshire, Colorado, Alabama and Virginia. Also found in large deposits in Canada and India.

Uses - Mica is used extensively as an insulating material in the construction of electrical apparatus. Used to take the place of windows (isinglass), for stove doors, lanterns, etc. Powdered mica is used to give wall paper a shiny luster, as a non-conductor of heat, as a lubricant in oils, and as a fireproofing material.

Q.   GARNET

The garnets, of which there are six varieties, are complex silicates of the metals calcium, magnesium, iron, manganese, aluminum and chromium. The name garnet is derived from the Latin word granatus, meaning like a grain.

Composition - The variety of garnet known as almandite is a silicate of iron and aluminum, Fe3Al2(SiO4)3. The other varieties of garnet have a similar a formula with the iron and aluminum replaced by some of the other metals mentioned above.

garnet # 1
Crystal System-Usually as the rhombohedron (Fig. 36) and the trapezohedron (Fig. 37).


GILBERT BOY ENGINEERING

garnet # 2
Structure - Usually well crystallized. Also massive and coarse to fine grained.

Physical Properties

Hardness - 6.5 to 7.5. Rather hard. Will scratch window glass.
Specific Gravity - 3.9 to 4.2.
Luster - Vitreous. Resinous in some varieties.
Color - Deep red in almandite. In other varieties, yellow, brown, black, green and white.
Streak - White.

Experiment 17. How to Test for Garnet - Heat a small fragment of the mineral garnet (almandite), held in the forceps, in the reducing flame of the blowpipe and notice that the mineral fuses or melts.

Heat a small piece or fragment of the mineral on charcoal in the reducing flame of the blowpipe for several minutes. Allow the mineral to cool and notice that an iron globule has been formed. Try the effect of the magnet on the iron globule and observe that the globule is magnetic and is attracted by the magnet.

Garnets are generally recognized by their characteristic crystal forms, hardness and color.

Occurrence - The garnets are common minerals and very widely distributed. They occur as a constituent of many types of rocks. Sometimes found as rounded grains in stream and sea sands.

Almandite is found in India, Brazil, Australia, in the Alps and in Alaska. Some of the other varieties are found in Utah and Arizona, Bohemia, Ceylon, and in the Ural Mountains of Russia.

Uses - Some varieties of almandite are used as a gemstone. Garnets are sometimes used in the powdered state as abrasive material, as sand for grinding stone and for making sandpaper.


GILBERT MINERALOGY

R.    QUARTZ

Composition - Dioxide of silicon, SiO2. Silicon = 46.7 per cent, oxygen = 53.3 per cent. Frequently contains various impurities.
 
quartz # 1

Crystal System - Usually in the form of hexagonal prismatic crystals terminated by hexagonal pyramids. (Fig. 38). Sometimes the prism faces are missing, as in the form consisting of a doubly terminated hexagonal pyramid (Fig. 39).

quartz # 2
Structure - Common1y found as crystals. Also found massive, coarse to fine grained, Sometimes mammillary and stalactitic.

Physical Properties

Fracture - Conchoidal.
Hardness - 7. Rather hard. Easily scratches window glass.
Specific Gravity - 2.65 to 2.66.
Luster - Vitreous, sometimes resinous or greasy, transparent to opaque.
Color - Colorless when pure. When impure colored red, pink, yellow, amethyst, blue, green, black and brown.

Experiment 18. How to Test for Quartz - Heat a small piece of quartz,held in the forceps, in the blowpipe flame for several minutes and observe that the mineral does not fuse or melt. If the finely powdered mineral is fused with sodium carbonate on platinum or nickel-steel wire a clear glass bead is obtained.

Quartz is usually recognized by its glassy luster, crystal form. hardness and conchoidal fracture.

Varieties - A great many different varieties of quartz are found, the colors of which are due to the different impurities which they contain. Some of these are rose quartz, rock crystal, amethyst, smoky quartz, milky quartz and cat's eye. Other varieties are known as chalcedony, carnelian, chrysoprase, agate, onyx, flint. and jasper.


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Occurrence - Quartz is the most common of all the minerals. It is a very important constituent of most rocks. It is a very common vein mineral. It is associated commonly with muscovite and feldspar. It often occurs as an important ore of gold. Found in large amounts as sand in stream beds and upon the seashore and as a constituent of soils.

Very good quartz crystals are found in Arkansas and New York. Rock crystal is found in Ural Mountains, Brazil, on the shore of Lake Superior, Maine, Pennsylvania and South Dakota. Smoky quartz is found in Switzerland, Colorado, North Carolina and Maine. Agate is found in Brazil, Uruguay and in several places in the United States. Massive quartz is mined for various purposes in Connecticut, New York, Maryland and Wisconsin.

Uses - Many of the various forms such as amethyst, rose quartz, agate, etc., find important uses as ornamental material. Used in the form of quartz sand or sandpaper as an abrasive material. Used for making mortar and cement in form of sand, Has an important use in the manufacture of glass, porcelain, as a wood filler, scouring soaps and in paints. Some of its various forms such as quartzite and sandstone are used as a building stone and as a paving material. Quartz sand is used in large amounts as a flux in several smelting operations.

LIST OF THE MORE COMMON ELEMENTS WITH THEIR

SYMBOLS, ATOMIC WEIGHTS AND VALENCES

Element Symbol Atomic
Wgt
Valence
Aluminum
Antimony
Argon
Arsenic
Barium
Bismuth
Boron 
Bromine
Cadmium
Calcium
Carbon
Chlorine
Chromium
Cobalt
Copper
Fluorine
Gold 
Helium 
Hydrogen
Iodine
Iron
Lead 
Lithium  
Magnesium 
Manganese 
Mercury
Nickel 
Nitrogen
Oxygen
Phosphorous
Platinum 
Potassium
Silicon 
Silver
Sodium
Strontium
Sulphur
Tin 
Zinc 
Al  
Sb
A
As
Ba
Bi
B
Br
Cd
Ca
C
Cl
Cr
Co
Cu
F
Au 
He
H
I
Fe
Pb
Li
Mg
Mn
Hg
Ni
N
O
P
Pt
K
Si
Ag
Na
Sr
S
Sn
Zn
27
120
40
75
137
208
11
80
112
40
12
35
52
59
63
19
197
4
1
127
56
207
7
24
55
200
59
14
15
31
195
39
28
108
23
87
32
119
65
3
3, 5

 3, 5
2
 3, 5
3
1
2
2
4
1
2, 3, 4
2
1, 2
1
1, 3

1
1
2, 3
2, 4
1
2
2, 4
1, 2
2
3, 5
 2
3, 5
4
1
4
1
1
2
2, 4, 6
2, 4
2


GILBERT MINERALOGY

LIST OF SOME COMMON MINERALS

WITH THEIR FORMULAE

Albite
Amphibole
Apatite
Arsenopyrite
Barite
Biotite
Bornite
Calamine
Calcite
Cassiterite 
Celestite
Cerussite
Chalcocite
Chalcopyrite
Cinnabar
Corundum
Cuprite
Dolomite
Epidote
Fluorite
Galena
Garnet
Graphite
Halite
Hematite
Kaolinite
Limonite
Magnetite
Malachite
Muscovite
Natrolite
Orthoclase
Pyrite
Pyrolusite
Pyroxene
Quartz
Serpentine
Siderite
Smithsonite
Sphalerite
Staurolite
Stibnite
Talc
Tetrahedrite
Tourmaline
sodium aluminum silicate
calcium and magnesium silicate
fluoride and phosphate of calcium
sulpharsenide of iron
barium sulphate
complex silicate of aluminum, iron, magnesium and potassium
copper iron sulphide
zinc silicate
calcium carbonate
tin oxide
strontium sulphate
lead carbonate
cuprous sulphide
iron and copper sulphide
mercuric sulphide
aluminum oxide
cuprous oxide
calcium magnesium carbonate
complex silicate of calcium, aluminum and iron.
calcium fluoride
lead sulphide
complex silicate of iron, magnesium, aluminum and calcium
carbon
sodium chloride
iron oxide
complex aluminum silicate
iron oxide
iron oxide
basic copper carbonate
complex silicate of potassium and aluminum
complex silicate of sodium and aluminum
potassium aluminum silicate
iron disulphide
manganese dioxide
calcium magnesium silicate
silicon dioxide
magnesium silicate
iron carbonate
zinc carbonate
zinc sulphide
complex silicate of iron and aluminum
antimony sulphide
magnesium silicate
antimony copper sulphide
complex silicate of boron and aluminum
NaAlSi3O8


FeAsS
BaSO4

Cu5FeS4.

CaCO3
SnO2
SrSO4
PbCO3
Cu2S
CuFeS2
HgS
Al2O3
Cu2O
CaMg(CO3)2

CaF2
PbS

C
NaCl
Fe2O3

2Fe2O3 3H2O
Fe3O4
CuCO3Cu(OH)2



FeS2
MnO2

SiO2

FeCO3
 ZnCO3
ZnS

Sb2S3

Cu8Sb2S7


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