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Aluminum, a metal which does not occur in nature in the free state, but for the most part in combination with silica, as a silicate of aluminum, in clay and many minerals. As extracted from clay by a series of very difficult chemical operations, it forms a white metal, very ductile and malleable, and susceptible of a high polish. On account of its lightness, aluminum is highly valued; it forms excellent alloys.

Bauxite (aluminum hydrate) is the only ore. It is mined in France, Ireland, Austria, Arkansas, Alabama and Georgia, and is refined by electric processes. It is used largely as an addition to iron and steel, preventing bubbles and waste in castings; in electrical work, and for purposes where a light, strong metal is necessary, as in certain machinery, hulls for small boats, etc. Refineries are located in Switzerland, France, Great Britain and United States.

Cryolite (fluoride of aluminum and sodium), a mineral mined only in Greenland, was formerly used as an ore but is now utilized in the manufacture of alum and soda.

Alum (a sulphate) is made from cryolite or clays.

Corundum (aluminum oxide) is, next to the diamond, the hardest natural mineral. Canada, North Carolina, Alabama and India have mines of corundum. Emery is produced chiefly in Greece and Asia Minor. Corundum and emery are powdered for use as abrasives in wheels, sharpening stones, polishing powder and cloth.

Emery is an impure form of corundum.

Feldspar is a silicate of aluminum with other metals. It is mined in Canada, Pennsylvania, Connecticut, New York, Maine and Norway, and ground up for use in pottery making.

Clay is chiefly silicate of aluminum and other metals. Kaolin is its purest form. The properties of clay vary with its composition, as china clay, fire clay, pipe clay, brick clay. Clays are found in all parts of the world as a result of the decomposition of other rocks.

The location of manufacturing centers of pottery of all kinds and of bricks, is dependent on clay deposits. In pottery making, Ohio, New Jersey and Pennsylvania lead the United States. Abroad, fine china is made in France, Germany, Austria, England, Japan, and China.

TABLE FOR THE IDENTIFICATION OF COMMON MINERALS; THEIR SCIENTIFIC AND COMMON NAMES AND CHIEF CHARACTERISTICS

Name of Mineral	Common Name	Composition	Hardness	Lustre	Color	Streak	Cleavage or Fracture	Crystallization and Occurrence	Tenacity etc.	Diaphaneity	Varieties	Remarks
Amphibole. (ăm´fĭ-bōl)	…	Silicate of magnesium, calcium, aluminum, iron, etc.	5–6	Glassy to dull.	Black or light to dark green.	White.	Perfect in two directions at angle of 124°.	Prismatic crystals with hexagonal cross-section, common; also cleavable masses.	Brittle to tough.	Opaque to transparent.	Actinolite (green, transparent). Asbestos (fibrous, dull). Hornblende (black).	Common constituent of igneous and metamorphic rocks. Valueless.
Arsenopyrite. (är´sĕn-ō-py̆r´īt)	Mispickel.	Sulphide and arsenide of iron.	6	Metallic.	Silver, yellowish, or light grayish white.	Black.	Good in two directions at an angle of 112°. Not evident on fine grained material.	Crystals resemble a double-edged axe. Occurs also coarse to fine granular.	Brittle.	Opaque.	…	Principal ore of arsenic and sometimes carries gold. Gives sparks and garlic odor when struck with a hammer. Yellow tarnish.
Barite. (bā´rīt)	Barytes. Heavy spur.	Sulphate of barium.	3	Glassy to stony.	White, yellow, blue or brown.	White.	Perfect in one direction; two other good cleavages at right angles to the first and at 101° with each other.	Diamond shaped or rectangular tabular, or prismatic crystals and platy masses.	Brittle.	Transparent to translucent.	…	Used to adulterate white lead and give weight to paper. Often associated with lead ores. Very heavy.
Biotite. (bī´ō-tīt)	Black Mica.	Hydrous silicate of aluminum, potassium, magnesium and iron.	21⁄2−3	Glassy to almost metallic.	Black or dark brown.	White.	Very perfect in one direction, yielding thin sheets.	Six-sided tabular crystals, and as scales, plates, or scaly masses.	Flexible and elastic.	Opaque to transparent.	…	Common constituent of igneous rocks. May be brittle when altered. Valueless.
Calcite. (kăl´sīt)	Lime. Calespar.	Carbonate of Calcium.	3	Glassy to earthy.	Colorless or white when pure, all colors when impure.	White.	Perfect in three directions at angles of about 105° or 75°.	Prismatic or tabular six-sided crystals; also granular, cleavable, or earthy masses.	Brittle.	Transparent to opaque.	Marble (granular). Limestone (dull, compact). Chalk (soft, white, earthy). Mexican Onyx (compact, banded).	Effervesces vigorously in hydrochloric acid of any strength and temperature. Used as flux, building or ornamental stone, to make lime, etc.
Chalcocite. (kăl´kŏ-sīt)	Copper Glance.	Sulphide of copper.	3	Metallic; dull when impure or tarnished.	Dark gray. Tarnishes black or green.	Lead-gray.	No cleavage, smooth conchoidal fracture.	Usually very compact masses; six-sided, tabular crystals rare.	Slightly sectile.	Opaque.	…	An important ore of copper. Cuts easily, yielding a highly polished surface.
Chalcopyrite. (kăl´kō-pĭr´īt)	Copper Pyrites. Fools gold.	Sulphide of copper and iron.	4	Metallic.	Bright brass-yellow. Often tarnished iridescent.	Greenish black.	No cleavage. Uneven fracture.	Occurs massive or in scattered particles. Crystals usually have four triangular faces.	Brittle.	Opaque.	…	One of the most important ores of copper and often carries silver and gold. Is often mistaken for the latter.
Copper.	…	Native metallic copper.	21⁄2−3	Metallic.	Copper-red. Tarnishes green to black.	Copper-red.	No cleavage. Hackly fracture.	Masses, plates, scales, branching aggregates and octahedral crystals, usually distorted.	Malleable sectile.	Opaque.	…	The value and uses of copper are well known. Often carries some silver.
Corundum. (kō-rŭn´dŭm)	…	Oxide of aluminum.	9	Glassy.	All colors; usually gray or brown when massive.	White.	Often parts readily into almost rectangular pieces whose faces are cross-hatched.	Prismatic or tabular six-sided crystals; also granular and pseudo-cleavable masses.	Brittle to tough.	Translucent to transparent.	Ruby (red). Sapphire (blue, etc.). Adamantine. Spar (massive). Emery (granular, impure).	A very valuable gem mineral and a fine abrasive. See plate I, figures 10, 11 and 13.
Epidote. (ēp´ĭ-dōt)	…	Basic silicate of calcium, aluminum and iron.	6–7	Glassy to dull.	Dark green or greenish brown (crystals) to light yellowish green.	White.	Perfect in one direction.	Slender, deeply grooved prismatic crystals and cleavable to fine granular masses.	Brittle.	Transparent to opaque.	…	Common constituent of metamorphic rocks. Rarely cut as a gem.
Fluorite. (flōō´or-īt)	Fluor Spar. Fluorine.	Calcium fluoride.	4	Glassy.	All colors; green, violet, purple, colorless and white, the commoner.	White.	Cleaves easily into octahedrons, i.e., in four directions, at angles of 109° or 71°.	In groups of crystals, usually cubical; also in cleavable masses. Sometimes granular.	Brittle.	Transparent to translucent.	Rock fluorite (finely granular and usually very impure and hard).	Used as a flux in smelting ores, and in several arts and trades.
Galenite. (gȧ-lē´nīt)	Galena. Lead.	Sulphide of lead.	3	Metallic.	Bluish lead, gray. Tarnishes black.	Lead-gray.	Perfect cubical, i.e., in three directions at angle of 90°.	Cubical crystals, often with triangular faces on the corners; also, cleavable to granular masses.	Very Brittle.	Opaque.	Steel galena (very fine grained masses). Often rich in silver.	Most important lead and silver ore. Often contains the latter metal with sometimes gold and other elements.
Garnet.	…	Silicate of various elements: calcium, aluminum and iron are commonest.	61⁄2−71⁄2	Glassy to resinous.	Commonly some shade of red; also brown, yellow, white, black, green.	White.	No cleavage. Uneven fracture.	Complex, rounded crystals, glassy masses and granular.	Brittle.	Transparent to opaque.	…	An important abrasive and a beautiful gem. Found in metamorphic rocks. See plate I, figures 8 and 15.
Gold.	…	Native metallic gold with a little silver, copper, etc.	21⁄2−3	Metallic.	Golden yellow to nearly silver-white.	Yellow to nearly white.	No cleavage. Hackly fracture.	Nuggets, plates, scales, wires; branching aggregates and distorted crystals, usually octahedral.	Malleable sectile.	Opaque.	Based upon and named after any impurities that may be present.	The value and uses of gold are well known.
Graphite. (graph´īt)	Black Lead. Plumbago.	Carbon.	1–2	Metallic to dull.	Dark gray to black.	Dark gray.	Perfect in one direction. Cleavage faces are apt to be curved. Not shown if finely granular.	Imbedded scales and foliated, granular or compact masses. Rarely in six-sided, tabular crystals.	Sectile Flexible.	Opaque.	…	Used in the manufacture of lubricants, infusible crucibles, and “lead” pencils.
Gypsum. (jĭp´sŭm)	…	Hydrous sulphate of calcium.	11⁄2−2	Pearly, silky, vitreous, dull.	White, gray, red, yellow or other tints due to impurities.	White.	Very perfect in one direction; two others show as cracks at angle of 114°, on the perfect cleavage faces.	Diamond shaped crystals, and cleavable, fibrous, granular, foliated or compact masses.	Sectile, Thin flakes, flexible.	Translucent to transparent.	Selenite (cleavable, transparent). Satin spar (white, fibrous, silky). Alabaster, (white, fine grained).	Is carved into vases, statues, etc., and forms plaster of paris when calcined and ground. Is a precipitate rock.
Halite. (hā´līt)	Rock salt.	Chloride of sodium.	21⁄2	Glassy.	Colorless or white when pure. Yellow, brown, red, etc., when impure.	White.	Perfect cubic i.e., in three directions at angle of 90°.	Cubical or octahedral crystals; also cleavable, granular or compact masses.	Brittle.	Translucent to transparent.	…	Tastes salty. Enormous quantities are used to season food, in various arts and trades, and as a source of sodium and its salts. A precipitate rock.
Hematite. (hēm´ȧ-tīt)	Red oxide of iron.	Oxide of iron.	51⁄2−61⁄2	Metallic to earthy.	Black when metallic; reddish black when dull, red when earthy.	Red.	No cleavage; may have a parting in one direction producing a platy structure. Uneven fracture.	Complex, tabular or rounded crystals; also platy, oolitic, earthy, micaceous, and kidney shaped masses.	Brittle.	Opaque.	Specular iron (mirror-like plates or crystals). Red Ochre or Ruddle (red, earthy).	The most important ore of iron, and is also used to make cheap paint, polishing powder, etc.
Limonite. (lī´mŏn-īt)	Yellow oxide of iron.	Hydrous oxide of iron.	5–51⁄2	Dull, silky, varnish-like.	Yellow, brown or nearly black.	Yellow or yellowish brown.	No cleavage. Uneven fracture.	Botryoidal or stalactitic forms with a radiating fibrous structure and a varnish-like surface, also earthy masses and concretions.	Brittle.	Opaque.	Bog iron ore (porous, earthy, often encloses vegetation). Yellow ochre or umber (earthy with clay, etc.).	Commonest, but most impure ore of iron, and is also used to make cheap yellow and brown paint.
Magnetite. (mag´net-īt)	Magnetic iron ore.	Oxide of iron.	51⁄2−61⁄2	Metallic to dull.	Iron-black.	Black.	No cleavage. Sometimes parts in four directions at angles of 109° and 71°. Uneven to subconchoidal fracture.	Octahedral crystals, and coarse to fine granular, laminated, or compact masses.	Brittle.	Opaque.	Lodestone (a natural magnet).	The only black, brittle, magnetic mineral, and a very pure and valuable ore of iron.
Malachite. (măl´ȧ-kīt)	…	Hydrous carbonate of copper.	31⁄2−4	Silky to dull.	Green, often nearly black on exposed surfaces.	Green. Paler than the color.	No cleavage. Uneven fracture.	Massive, as botryoidal crusts with a radiating structure and silky lustre, and as slender crystals forming velvety surfaces.	Brittle.	Translucent to opaque.	…	Is an ore of copper and is used as an ornamental stone and in jewelry. Azur-malachite is malachite mixed with blue azurite. See plate I, figure 4.
Muscovite. (mŭs´ko̱vīt)	Mica, isinglass. White Mica.	Hydrous silicate of potassium and aluminum.	2–21⁄2	Glassy. Pearly on cleavage faces.	White or light tints of other colors, particularly gray, brown or green.	White.	Very perfect in one direction, yielding thin sheets.	Six-sided, tabular crystals, and as scales, plates, or scaly masses.	Flexible and elastic.	Transparent to translucent.	…	Used in stove doors, as insulation in electrical apparatus, and for spangling or frosting paper and fabric.
Orthoclase. (ôr´tho̱-klās)	Feldspar. Potash.	Silicate of potassium and aluminum.	6	Glassy to stony.	Flesh-red, gray, yellow, white or colorless.	White.	In two directions at angle of 90°, one direction slightly less perfect than the other.	Thick-set square or six-sided crystals, or cleavable masses or grains.	Brittle.	Transparent to opaque.	Sanadine (transparent crystals or grains imbedded in igneous rocks).	Associated with quartz and mica in many rocks. Used in making glass and porcelain. Next to quartz in frequency of occurrence.
Pyrite. (pĭr´īt)	Pyrites. White iron. Fools gold.	Sulphide of iron.	6–61⁄2	Metallic.	Pale to deep brass-yellow. Tarnishes brown or iridescent.	Black.	No cleavage. Conchoidal to uneven fracture.	Cubical, octahedral, or complexly rounded crystals, coarse to fine granular, and massive.	Brittle.	Opaque.	…	Used in making sulphuric acid and often contains so much gold, silver and copper as to make it an ore of these metals.
Pyrolusite. (pĭr´o̱-lū´sīt)	…	Oxide of manganese.	1–21⁄2	Metallic to dull.	Black to dark steel-gray.	Sooty black.	May appear to have good cleavage in one direction but usually shows none.	Occurs as radiating prismatic layers, velvety crust and granular to compact masses. Soils the fingers.	Brittle.	Opaque.	…	Has many uses and is valuable. Usually associated with a very fine grained, hard, black mineral that is often botryoidal.
Pyroxene. (pĭr´ŏks-ēn)	…	Silicate of magnesium, calcium, aluminum and iron.	5–6	Glassy to dull.	Black or light to dark green.	White to greenish.	Poor in two directions at angle of nearly 90°. May have a fine platy parting.	Prismatic crystals with square or octagonal cross-section; also foliated and massive.	Brittle.	Transparent to opaque.	Diopside (light green, glassy). Diallage (light green, dull, foliated). Auagite (black).	A common constituent of igneous rocks. Diopside is sometimes used as a gem.
Quartz. (Pheno- crystalline).	…	Oxide of silicon.	7	Glassy.	White or colorless when pure. All colors when impure.	White or light tints.	No cleavage. Single crystal has conchoidal fracture, otherwise the fracture is uneven.	Six-sided prism terminated by a six-sided pyramid; also massive, coarse to fine granular, and as sand.	Brittle.	Transparent.	Rock crystal (colorless, transparent). Amethyst (purple). Rose (pink). False topaz or Citrine (yellow). Smoky quartz or Topaz (brown or gray). Milky (white). Ferruginous (iron stained).	The commonest of all minerals. A constituent of most rock. Great quantities are used as a flux in smelting, as abrasives, and in the manufacture of glass and porcelain. The transparent varieties of pleasing tints are used as gems. Water-clear spheres are very valuable.
Quartz. (Crypto- crystalline).	…	…	…	Dull to earthy.	…	…	No cleavage. Conchoidal fracture.	Very fine grained massive, botryoidal, nodular, or filling or lining cavities in rocks.	Brittle.	Translucent to opaque.	Chalcedony (drab). Carnelian (red, translucent). Jasper (red, brown, yellow, opaque). Heliotrope or Bloodstone (dark green with red spots). Flint (dark gray concretions). Agate (banded or particolored). Onyx (agate with flat layers). Petrified wood (wood replaced by quartz).	…
Serpentine. (sēr´pēn-tīn)	…	Hydrous silicate of magnesium and iron.	4+	Wax-like, silky, earthy.	Light to dark green, yellow, brownish red, variegated.	White.	No cleavage. Conchoidal fracture when massive.	Compact, massive or coarse to fine fibrous. The two habits are often in parallel layers.	Tough. Fibres are flexible.	Translucent to opaque.	Precious or noble (massive, translucent). Chrysolite (silky, fibres). Verde antique (massive with calcite).	Chrysolite is the best commercial asbestos. Other varieties are used as ornamental stone and occasionally in jewelry.
Siderite. (sĭd´ẽr-īt)	…	Carbonate of iron.	31⁄2−4	Glassy to earthy.	Light to dark brown or gray. Tarnishes reddish brown or brownish black.	White to yellowish.	Very perfect in three directions at angle of 107° and 73°. Not evident when fine grained.	Cleavable masses, coarse to fine, granular and at warped crystals that resemble distorted cubes.	Brittle.	Translucent to opaque.	Sphaerosidirite or Clay-ironstone (concretions of fine grained siderite mixed with clay).	The most valuable ore of iron, but is rather uncommon. The impure clay-ironstone is fairly common in sediments.
Sphalerite. (sfāl´ẽr-īt)	Blende, Jack Rosin zinc, zinc, etc.	Sulphide of zinc.	31⁄2−4	Resinous to nearly metallic.	Commonly yellow, brown, black or red; sometimes green or white.	White, yellow or brown.	Very perfect in six directions at angles of 60°, 90° and 120°.	Complexly rounded or modified cubical crystals; also cleavable, coarse to fine granular masses, and botryoidal, etc.	Brittle.	Transparent to opaque.	…	The commonest zinc ore and an impure variety furnishes most of the cadmium of commerce. Associated with galenite and silver minerals.
Stibnite. (stĭb´nīt)	…	Sulphide of antimony.	2	Metallic.	Light gray. Cleavage faces appear silver white when reflecting light.	Lead-gray.	Perfect in one direction, yielding blade-like strips which are bent or hatched perpendicular to their length.	Sharp, vertically grooved, prismatic crystals and in cleavable masses with a bladed structure.	Very brittle.	Opaque.	…	The chief source of antimony and its salts. Sometimes carries gold and silver.
Talc. (tălk)	Talcum.	Hydrous silicate of magnesium.	1–11⁄2	Waxy to dull. Pearly on cleavage faces.	White, light green, gray; other colors when impure.	White to greenish.	Perfect in one direction, yielding thin flexible plates. Not shown on the fine grained soapstone.	Foliated, coarse to fine granular, or compact masses. Feels greasy to soapy.	Tough sectile.	Transparent to translucent.	Steatite or soapstone (granular, impure, hardness up to 21⁄2). French chalk (white, fine grained soft).	Used in making porcelain, polishing powder, lubricants, gas jets, tinted plasters, paper, soap, leather dressing, talcum powder, slate pencils, and in other ways.
Tetrahedrite. (tet´ra-he´drīt)	Gray copper.	Sulph-antimonite of copper.	3–41⁄2	Metallic.	Gray.	Gray, brown, or reddish.	No cleavage. Uneven, granular fracture.	Crystals have four triangular faces. Occurs usually granular massives.	Brittle.	Opaque.	…	Often contains enough silver to make it a valuable ore of this metal as well as copper.
Tourmaline. (tōōr´mȧ-lĭn)	Schorl.	Silicate of boron and various other bases varying with the variety.	7–71⁄2	Glassy to resinous.	All colors. Interior and exterior or opposite ends of a crystal may differ in color.	White.	No cleavage. Uneven to poor conchoidal fracture.	Vertically lined, prismatic crystals with spherical triangular cross-sections. Also columnar or compact massive.	Very brittle.	Transparent to opaque.	Schorl (black). Rubellite (pink). Indicolite (blue). Achroite (white).	A popular semi-precious gem. When heated (not above 212° F.), will usually pick up bits of paper. Opposite ends of crystals have different forms.
Zoisite. (zois´īt)	…	Silica, alumina, lime, peroxide of iron, water.	6	Pearly.	White, gray, yellow, brown.	Uncolored.	Parallel cleavage; sometimes fibrous.	Occurs in tri-metric crystals; also massive.	Brittle.	Transparent, translucent.	…	Often a constituent of metamorphic rocks.