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Gummite: An alteration product of Uraninite—composition doubt­ful. It occurs in crystalline form and in rounded and flattened pieces looking like gum. Color is reddish-yellow to orange or hyacinth-red; feebly translucent. It occurs in pitchblende at Joachimsthal, and is abundant at the Flat Rock mine, in Mitchel County, North Carolina, and also in other localities with Uraninite, a source of radium salts. (See Radium.)
Gypsum: Hydrous Calcium Sulphate. Sulphur 46.6%, Lime 32.5%. This mineral, the most important of the hydrous sulphates, occurs in masses associated with limestone, in crystals, fibrous, and in granular aggregates. It is white, color­less and transparent when pure; gray, red, yellow, blue or black when impure. The crystallized transparent variety is called Selenite, some of the crystals containing a so-called "bubble" Crude Gypsum is used in the manufacture of plaster, as a retarder in Portland cement, and as a fertilizer. Small quantities are used in glass manufacture; also as a whitewash; as a deodorizer; and as an adulterant in candy and other foods. It is sometimes used as a medium of sculpture. A white massive variety, known as Alabaster, is used for carving ornaments, and lamps.
After the United States, France is the largest producer of gyp­sum. Burnt gypsum is called "Plaster of Paris," because the Mont-martre gypsum quarries are near Paris, and are famous for supplying it.
Halite: Sodium Chloride. Common or rock salt. This mineral oc­curs in cubes and crystals, also as massive and granular, is white or colorless; also yellow, reddish, bluish and purp­lish. It is the best known and most abundant native chloride, is soluble and the taste, saline. Salt is used for the preservation of organic substances, is employed in glazing pottery, in metallurgical processes, for clearing oleomargarine, in making butter and in the more familiar household operations.
Halite is the chief source of sodium compounds and is found in large quantities at Saginaw, Michigan; also in New York, California, Utah, Kansas, Missouri and many places in Europe, especially at Stassfurt, Germany.
Harmotome: Barium Compound. Occurs in crystals, and forms complex groups of twins. Color, white, gray, yel­low, red or brown. It is found at Strontian, Scot­land, in fine crystals some an inch thick; also at Norway, Silesia, and in the Harz Mountains. In the United States, small crystals were found while excavating the Fourth Avenue tunnel in New York City. They are also found on the north shore of Lake Superior.
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