Gypsum resources of Indiana (1969)

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Authors: Robert French
Lawerence Rooney

4), a mineral that hydrates slowly to gypsum. Although anhydrite is considered mainly an impurity in gypsum deposits, it has limited use as a retarder in cement and as a source of sulfuric acid. Its typical dark-blue color laced with veinlets of gypsum would make it an attractive interior veneer, but to our knowledge it has no use as such. Because gypsum has low unit value, transportation is a large part of its cost to the consumer, and the location of a deposit plays a major role in determining its economic value. In the arid west, where gypsum can be found at or near the surface, some good deposits go begging because the market is small. In the east, where groundwater has leached gypsum as deep as several hundred feet, gypsum deposits of moderate purity are economic because the market is large. The southeastern United States especially is lacking in gypsum deposits and is supplied largely by gypsum in southwestern Indiana in the early 1950's, therefore, was a major find and has been called "one of the few important discoveries of gypsum made in North America in recent decades" (Harvard, 1957, p. 58). That evaluation applies equally well to the deposits of gypsum in southern and northern Indiana differ in age, mining problems, and stage of development, as well as geography, they will be discussed separately. In this chapter the term evaporites is restricted to mean gypsum and anhydrite and the term minable evaporites to mean any evaporite unit: (1) that may contain more than 80 percent evaporites, (2) that is more than 10 feet thick, and (3) that in places may be completely gypsified. These definitions are not intended to imply that gypsum less than 80 percent pure, gypsum beds less than 10 feet thick, and anhydrite could not be mined economically." style="width:400px; height:120px;">INTRODUCTION: Gypsum is a common, abundant mineral composed of hydrated calcium sulfate (CaSO4.2H2O), which upon heating to moderate temperatures loses most of its water to form calcium sulfate (CaSO4.1/2H2O). Upon the addition of water, the hemihydrate becomes plastic for a short time and then reverts to gypsum. Because of this "setting" property, gypsum has found wide use as a building material, first as plaster and now dominantly as wallboard and lath. Gypsum is also used in its raw form, mostly as a retarder in portland cement and a soil conditioner (land plaster). In its natural state, gypsum is generally associated wtih anhydrite (CaSO4), a mineral that hydrates slowly to gypsum. Although anhydrite is considered mainly an impurity in gypsum deposits, it has limited use as a retarder in cement and as a source of sulfuric acid. Its typical dark-blue color laced with veinlets of gypsum would make it an attractive interior veneer, but to our knowledge it has no use as such. Because gypsum has low unit value, transportation is a large part of its cost to the consumer, and the location of a deposit plays a major role in determining its economic value. In the arid west, where gypsum can be found at or near the surface, some good deposits go begging because the market is small. In the east, where groundwater has leached gypsum as deep as several hundred feet, gypsum deposits of moderate purity are economic because the market is large. The southeastern United States especially is lacking in gypsum deposits and is supplied largely by gypsum in southwestern Indiana in the early 1950's, therefore, was a major find and has been called "one of the few important discoveries of gypsum made in North America in recent decades" (Harvard, 1957, p. 58). That evaluation applies equally well to the deposits of gypsum in southern and northern Indiana differ in age, mining problems, and stage of development, as well as geography, they will be discussed separately. In this chapter the term evaporites is restricted to mean gypsum and anhydrite and the term minable evaporites to mean any evaporite unit: (1) that may contain more than 80 percent evaporites, (2) that is more than 10 feet thick, and (3) that in places may be completely gypsified. These definitions are not intended to imply that gypsum less than 80 percent pure, gypsum beds less than 10 feet thick, and anhydrite could not be mined economically.



French, R. R., Rooney, L. F. 1969,  Gypsum resources of Indiana: Indiana Geological Survey Bulletin 42A, 34 p., 20 fig.


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Keywords: gypsum, industrial minerals, anhydrite

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