Gypsography

[Lat. gypsum, and Gr. graphe, a writing.] The act or art of writing or inscribing on gypsum. Gypsum, (jip's um,) n. [Gr. gupsos , especially the calcined mineral, perhaps from ge , earth, and hepseo, to cook.] (Min.) A hydrous sulphate of lime, which crystallizes usually in right rhomboidal crystals with levelled sides. It occurs also in laminated ma es, in fibrous ma es with a satin lustre, and in radiating forms consisting of narrow lam inæ, also granular and compact. Color usually white, but sometimes gray, reddish, brownish, yellow, blue, and even black. Sp . gr ., when pure, 2-314-2-328. Comp . Sulphuric acid 46-5, lime 33-6, water 20-9. G. occurs in extensive beds in several of the U. States, particularly in N. York, Ohio, Illinois, Virginia, Tenne ee, and Arkansas, and is usually a ociated with salt springs. It occurs especially in connection with limestones and marlytes or clay beds. It is a product of volcanoes found where sulphur gases are escaping, being formed from the sulphuric acid generated and the lime of decomposing lavas. When lime is present it is formed by the decomposition of pyrite. It occurs about sulphur springs where sulphuretted hydrogen is emitted, and is found in sea-water. In the Mammoth Cave G. occurs in the form of rosettes or flowers, vines or shrubbery. When burned and ground, it is called PLASTER OF PARIS, (q. v.) The transparent foliated G. is called SELENITE, (q. v.) The white and delicately fibrous variety is de scribed under the head of SATIN SPAR (q. v.); and the fine-grained, white or light colored varieties, under the head of ALABASTER (q.v.). G. is ground up and applied to soils as a fertilizer. When destitute of water it is called ANHYDRITE (q.v.). Gypsum, in Ohio, a post-office of Ottawa co. Gypsum Creek, in Michigan, enters Grand River abt. 3 m. below Grand Rapids.