Sulfates are elements combined with both sulfur and oxygen, such as gypsum, barite, and anglesite.
Crystal system: orthorhombic. Cleavage: often in groups of platy or tabular crystals. Color: usually white, but may be light shades of blue, brown, yellow, or red. Hardness: 3.0-3.5. Streak: white. Luster: vitreous to pearly. Specific gravity: 4.5. Tenacity: brittle. Uses: in heavy muds in oil-well drilling, to increase brilliance in glass-making industry, as filler for paper, cosmetics, textiles, linoleum, rubber goods, paints.
Barite generally occurs in the white massive variety (often appearing earthy when weathered), although some clear to bluish, bladed barite crystals (Plate 18) have been observed in several vein deposits in central Kentucky, and various nodular zones have been observed in Silurian-Devonian rocks in east-central Kentucky. Rosettes are common in many Kentucky mineral veins. Feathery barite is also known from Kentucky.
Barite is extremely insoluble in acid and water and is therefore chemically inert. It is the principal source of the element barium. Barite is the most abundant of the semi-commercial vein-forming minerals in central Kentucky. Until World War I, barite was mined along with fluorite and sphalerite in Jessamine, Woodford, and Fayette Counties. Limited barite mining was attempt during the 1960's in Lincoln and Boyle Counties. Commercial barite was recovered as a by-product of the fluorspar industry in western Kentucky during World War II and during the 1960's.
For more detailed information see Vein Mineral Deposits.
Crystal system: orthorhombic. Cleavage: tabular or prismatic. Color: generally white, but may be tinted blue or pink. Hardness: 3.0-3.5. Streak: white. Luster: glassy to pearly. Specific gravity: 3.9. Tenacity: brittle. Uses: fireworks, flares, tracer bullets, refining sugar beets, ceramic and glass industries, caustic soda solutions.
Celestite occurs as a solid-solution series with barite and is the principal ore of strontium. It is not common in Kentucky, but is sometimes found in vein deposits and lining cavities in limestones. Good celestite crystals have been found in nodules and geodes in Ordovician rocks in Woodford and Jessamine Counties, Silurian rocks in Montgomery County, and Mississippian rocks in Rockcastle and Lincoln Counties. The geodes are generally composed of an outer shell of siliceous material, such as chalcedony, and the inner parts are filled with celestite and associated minerals such as calcite, fluorite, barite, gypsum, and quartz.
Crystal system: monoclinic. Color: colorless when pure, but often stained gray to yellow. Hardness: 2.0. Streak: white. Luster: glassy. Specific gravity: 2.32. Uses: plaster, wallboard, pottery molds, orthopedic and dental plasters, portland cement.
Gypsum usually occurs as a massive variety, although crystals are common. A fibrous variety is called satin spar; it has a silky luster and is found as vein fillings and as thin layers in shales and limestones. Selenite is a transparent crystalline variety. Excellent selenite specimens and curved gypsum have been collected from the Lexington Quarry Company, where foot-long crystals have been discovered. The New Providence Formation in northwestern Marion County also has good gypsum crystals. The gypsum occurs as diamond-shaped crystals that often grow together to form "swallowtail twins." Numerous "gypsum flowers" adorn the walls of many caves in Kentucky.
From a commercial standpoint, rock gypsum is the most important variety. It is an aggregate of crystals that range from less than 0.1 mm to more than 2.0 mm in diameter. Bedded rock-gypsum deposits associated with anhydrite occur deep underground in the St. Louis Limestone in northwestern Kentucky and at moderate depths southwest of Louisville.
Anhydrite (crystal system: orthorhombic; color: white, gray, or bluish; hardness: 3.5; streak: white; luster: vitreous; specific gravity: 3.0) usually hydrates to gypsum. Anhydrite crystals have been found in well cuttings of deep oil wells, in nodules in Wayne County, and in some vein deposits.
Many other sulfates occur in lesser amounts in various parts of Kentucky. They are fragile, fibrous, granular or powdery, clear to white masses (except for copiapite). These minerals occur in coal beds, coal mines, and the black shale. Most of these minerals are difficult for the experienced collector to distinguish, and some may require analysis for correct identification. These minerals are humidity-sensitive and their chemistry may change when they are dehydrated. Epsomite is white and occurs as delicate encrustations. Melanterite is a white powdery mineral with glassy luster. Alunite is white and massive, and is distinguished from limestone and dolomite by not effervescing in an acid test. Copiapite occurs as a loose crust with a distinctive yellow color. Mirabilite forms white, massive crusts. Haliotrichite and pickeringite are massive and white, with silky luster and astringent taste.
Goslarite is a rare secondary zinc mineral that has been reported in the Western Kentucky Fluorspar District. It may be white to reddish, with good cleavage, and forms in acicular, orthorhombic crystals. Anglesite is white and soft, has a hardness of 3, and heavy specific gravity of 6.4. It is also rare but can be found in oxidized lead deposits.