480 



MINERALOGY. 



Foliated 

 granular 

 gypsum. 



Oryctogno- the folia, it melts into a white enamel, which, after a 



*J- time, falls into a white powder. 

 ^""Y ~* Constituent Paris. Lime, . . 33.9 



Sulphuric Acid, 43.9 

 Water, , 21.0 



Loss, . . 2.1100.0 

 Bncho'z, in Gehlen's Journ. b. v. s. 1 58. 

 Geognostic Situation. Occurs principally in the se- 

 condary or flo2tz gypsum formation, in thin layers : 

 less frequently in rock-salt ; more rarely as a constitu- 

 ent part of metalliferous veins ; but in considerable 

 quantity in that deposite known in the south of Eng- 

 land under the name of Blue or London Clay. Crys- 

 tals of this substance are daily forming in gypsum hills, 

 in old mines, and in mining heaps. 



Geographic Situation. It is not unfrequent in the blue 

 clay in the south of England, as at Shotover Hill, near 

 Oxford, and occurs in the secondary gypsum around 

 Paris. 



Uses. At a very early period, before the discovery 

 of glass, selenite was used for windows ; and we are 

 told, that, in the time of Seneca, it was imported into 

 Rome from Spain, Cyprus, Cappadocia, and even from 

 Africa. It is used for the finest kind of stucco, and the 

 most delicate pastil colours. When burnt, and perfectly 

 dry, it is used for cleansing and polishing precious 

 stones, work in gold and silver, and also pearls. 



SECOND SUBSPECIES. 



FOLIATED GRANULAR GYPSUM, Jameson. Blaettrig- 

 ger Gyps, Werner. 



External Characters Most common colours white, 

 grey, and red ; seldomer yellow, brown, and black. 

 Occurs massive, also in granular and prismatic distinct 

 concretions. Sometimes crystallized in small conical 

 lenses, in which the surface is rough. Lustre passes 

 from shining through glistening to glimmering, and is 

 pearly. Has the same cleavage as selenite. Fragments 

 very blunt-edged. Translucent. Sectile, and very 

 easily frangible. 



Constituent Parts. Lime, . 32 

 Sulphuric Acid, 30 

 Water, . 3898 Kirwan. 

 Geognostic Situation. It occurs in beds in primitive 

 rocks: in a similar repository in transition clay-slate; 

 but most abundantly in beds in rocks of the secondary 

 or flcetz class. 



Geographic Situation. It occurs in Cheshire and Der- 

 byshire ; at the Segeberg, near Kiel ; and at Liineburg, 

 where it contains crystals of boracite, and sometimes 

 of quartz ; and in many other parts of Europe. 



Uses. The foliated and compact subspecies of gyp. 

 sum, when pure, and capable of receiving a good po- 

 lish, are by artists named simply Alabaster, or, to dis- 

 tinguish them from calcsinter. or what is called calca- 

 reous alabaster, Gypseous Alabaster. The finest white 

 varieties of granular gypsum are selected by n< lists for 

 statues and busts: the variegated kinds are cut into 

 pillars, and various ornaments, for the interior of halls 

 and houses ; and the most beautiful variegated sorts 

 are cut into vases, columns, plates, and other kinds of 

 table furniture. Those varieties that contain imbedded 

 portions of selenite, when cut across, exhibit a beauti- 

 ful iridescent appearance, and are named Gypseous 

 Opal. In Derbyshire, and also in Italy, the very fine 

 granulai varieties are cut into large vases, columns, 

 , watch-cases, plates, and other similar articles. Both 

 subspecies are used in agriculture. Much difference of 

 opinion has prevailed among agriculturists with respect 



to the uses of gypsum. It is said to have been very Oryctogno- 

 advantageously employed in America, and also in the "? 

 county of Kent ; but it has failed in most of the other *"""Y" M1 *' 

 counties of England, though tried in various ways, 

 and for different crops. When peat-ashes contain a 

 considerable portion of gypsum, they may be advanta- 

 geously employed as a top-dressing for cultivated grass- 

 es, on such soils as contain little or no sulphate of lime. 

 The pure white varieties of granular gypsum are used 

 as ingredients in the composition of earthen-ware and 

 porcelain ; and the glaze or enamel with which porce- 

 lain is covered, has the purest gypsum, or even sele- 

 nite, as one of its ingredients, its most important use 

 is in the preparation of stucco. 



Tmnn SUBSPECIES. 



COMPACT GYPSUM, Jameson. DichterGyps, Werner. Compact 



External Characters Colours white, grey, blue, gypsum 

 red, and sometimes honey yellow. Occurs massive. 

 Generally dull, seldom feebly glimmering. Fracture 

 fine splintery, passing on the one side into even, on the 

 other into fine-grained uneven. Fragments indetermi- 

 nate angular, and blunt-edged. Translucent on the 

 edges. 



Chemical Characters. All the different varieties of 

 gypsum, when exposed to heat, are deprived of their 

 water of crystallization, become opaque, fall into a 

 powder, which, when mixed with water, speedily har- 

 dens on exposure to the air. They are difficulty fusi- 

 ble before the blowpipe, without addition, and melt 

 into a white enamel : when heated with charcoal, they 

 are converted into sulphuret of lime. 



Constituent Parts Lime, . 34 



Sulphuric Acid, 48 



Water, . ] 8_1 00 Gerhard. 



Geognostic Situation. Occurs in beds, along with 

 granular gypsum, selenite, and stinkstone, in the floetz 

 or secondary class of rocks. 



Geographic Situation. Occurs in the Campsie Hills; 

 Derbyshire ; Ferrybridge in Yorkshire; and Notting- 

 hamshire. 



FOURTH SUBSPECIES. 



FiBRousGvpsuM, Jameson. Fasriger Gyps, Werner. Fibroui 



External Characters Principal colours white, grey, gypsum, 

 red, and yellow. Occurs massive, and dentiform ; al- 

 so in fibrous distinct concretions, which are parallel, 

 generally straight, and sometimes curved. Lustre passes 

 from glistening, through -hining to splendent, and is 

 pearly. Fragments are long splintery. Translucent. 



Constituent Parts. Lime, 3.100 



Sulphuric Acid, 44 13 

 Water, 21.00 98.13 



Bacholz, N. Allg. Journ. d. Chem. 

 b v. H. ii. s 160. 



Gcognostic Situation ,It occurs along with the other 

 subspecies of this species. 



G "grnp/iic Si'uation It occurs in red sandstone 

 near Moffat; in red clay, on the banks of the Whit- 

 adder in Berwickshire ; in Dunbartonshire ; also in 

 Cumberland, Yorkshire, Cheshire, Worcestershire, Der- 

 byshire Somersetshire, and Devonshire. 



Ut>es. When cut rn cnbrxhon, and polished, it re- 

 flects a light not unlike that of the cat's-eye, and is 

 sometimes sold as that stone. It is also cut into neck- 

 laces, ear pendents, and crosses; and in this form it 

 is also sold for a harder mineral, the Fibrous Limestone, 

 or even imposed on the ignorant for that variety of 

 felspar named Moonstone. 





