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McGraw Hill Financial, Inc. is an American publicly traded corporation headquartered in Rockefeller Center in New York City. Its primary areas of business are financial, publishing, and business services.
A mineral consisting of calcium tungstate, CaWO<sub>4</sub>. Scheelite occurs in colorless to white, tetragonal crystals (see <b>illus.</b>); it may also be massive and granular. Its fracture is uneven, and its luster is vitreous to adamantine. Scheelite has a hardness of 4.5–5 on Mohs scale and a specific gravity of 6.1. Its streak is white. The mineral is transparent and fluoresces bright bluish-white under ultraviolet light.
Industry:Science
A mineral consisting of lead molybdate, PbMoO<sub>4</sub>. Wulfenite occurs commonly in yellow, orange, red, and grayish-white crystals. They may be tetragonal, tabular (see <b>illus.</b>), or pyramidal, with a luster from adamantine to resinous. Wulfenite may also be massive or granular. Its fracture is uneven. Its hardness is 2.7–3 and its specific gravity 6.5–7. Its streak is white. It is easily fusible and is decomposed by hydrochloric or nitric acid with the separation of molybdic oxide.
Industry:Science
A mineral having composition (Fe,Ni)<sub>9</sub>S<sub>8</sub>. Pentlandite is the major ore of nickel. It crystallizes in the isometric system, but crystals are rare. It is usually massive, showing a well-defined octahedral parting. The hardness is 3.5–4 (Mohs scale) and the specific gravity varies from 4.6 to 5.0, depending on the ratio of iron to nickel; greater amounts of iron cause an increase in the specific gravity. The luster is metallic and the color yellowish bronze. Pentlandite is usually associated with pyrrhotite, which it closely resembles in appearance, but the two can be distinguished by the octahedral parting and lack of magnetism of pentlandite. It is found at many localities in small amounts, but its chief occurrence is at Sudbury, Ontario, where it is mined on a large scale as a nickel ore.
Industry:Science
A mineral having composition Ag<sub>3</sub>AsS<sub>3</sub> and crystallizing in the hexagonal system. It occurs in prismatic crystals terminated by steep ditrigonal pyramids, but is more commonly massive or in disseminated grains. There is good rhombohedral cleavage. Hardness is 2–2.5 (Mohs scale) and specific gravity is 5.55. The luster is adamantine and the color ruby red. It is called light ruby silver in contrast to pyrargyrite, dark ruby silver. Proustite is less common than pyrargyrite but the two minerals are found together in silver veins. Noted localities are at Chañarcillo, Chile; Freiberg, Germany; Guanajuato, Mexico; and Cobalt, Ontario, Canada.
Industry:Science
A mineral having composition As<sub>2</sub>S<sub>3</sub> and crystallizing in the monoclinic system. Crystals are small, tabular, and rarely distinct (see <b>illus.</b>); the mineral occurs more commonly in foliated or columnar masses. There is one perfect cleavage yielding flexible folia which distinguishes it from other minerals similar in appearance. The hardness is 1.5–2 (Mohs scale) and the specific gravity is 3.49. The luster is resinous and pearly on the cleavage surface; the color is lemon yellow. Orpiment is associated with realgar and stibnite in veins of lead, silver, and gold ores. It is found in Romania, Peru, Japan, and Russia. In the United States it occurs at Mercer, Utah; Manhattan, Nevada; and in deposits from geyser waters in Yellowstone National Park.
Industry:Science
A mineral having composition BeAl<sub>2</sub>O<sub>4</sub> and crystallizing in the orthorhombic system. Chrysoberyl crystals are usually tabular parallel to the front pinacoid and frequently in pseudohexagonal twins (see <b>illus.</b>). There is good prismatic cleavage. The hardness is 8.5 (Mohs scale) and the specific gravity is 3.7–3.8. The luster is vitreous and the color various shades of green, yellow, and brown. There are two gem varieties of chrysoberyl. Alexandrite, one of the most prized of gemstones, is an emerald green but in transmitted or in artificial light is red. Cat's eye, or cymophane, is a green chatoyant variety with an opalescent luster. When cut en cabochon, it is crossed by a narrow beam of light. This property results from minute tabular cavities that are arranged in parallel position.
Industry:Science
A mineral having composition CdS (cadmium sulfide) and crystallizing in the hexagonal system (dihexagonal pyramidal class). Pyramidal crystals are rare, and greenockite usually occurs as earthy coatings with resinous luster and yellow-to-orange color. There is good prismatic cleavage; the hardness is 3 (Mohs scale) and specific gravity is 4.9. Greenockite and wurtzite, ZnS, are isostructural, and a complete solid-solution series exists between the two minerals. Although greenockite is the most common cadmium mineral, no deposits of it are sufficiently large to warrant mining it solely as a source of cadmium. It is commonly associated with sphalerite, and thus the supply of cadmium comes as a by-product from the treating of zinc ores.
Industry:Science
A mineral having composition FeSO<sub>4</sub>·7H<sub>2</sub>O. Melanterite occurs mainly in green, fibrous or concretionary masses or in short, monoclinic, prismatic crystals (see <b>illus.</b>). Fracture is conchoidal and luster is vitreous. Hardness is 2 on Mohs scale, and specific gravity 1.90. The mineral is similar to chalcanthite, has an astringent taste, and is readily soluble in water.
Industry:Science
A mineral having composition MnO<sub>2</sub>. Pyrolusite is the most important ore of manganese. It crystallizes in the tetragonal system but well-developed crystals (polianite) are rare. It is usually in radiating fibers or reniform coatings. The hardness is 1–2 on Mohs scale (often soiling the fingers) and the specific gravity is 4.75. Crystals of polianite show a perfect prismatic cleavage and have a hardness of 6 and a specific gravity of 5.1. The luster is metallic and the color iron-black. It frequently forms pseudomorphs after other manganese minerals, notably manganite.
Industry:Science
A mineral having composition NiS and crystallizing in the hexagonal system. Millerite usually occurs in hairlike tufts and radiating groups of slender to capillary crystals (see <b>illus.</b>). There is rhombohedral cleavage, but it is difficult to observe on the hairlike crystals. The hardness is 3–3.5 (Mohs scale) and the specific gravity is 5.5. The luster is metallic and the color pale brass yellow. Millerite forms at low temperatures, often in cavities and as an alteration of other nickel minerals. It is found in many localities in Europe, notably in Germany and the Czech Republic. In the United States it is found with pyrrhotite at the Gap Mine, Lancaster County, Pennsylvania; with hematite at Antwerp, New York; and in geodes in limestone at Keokuk, Iowa. In Canada large cleavable masses are mined as a nickel ore in Lamotte Township, Quebec.
Industry:Science
