238 



DESCRIPTIVE MINERALOGY. 



Fig. 103. 



The finest specimens of the fohated variety, the Selenite, or Isinglass plaster, as it is 

 usually called, in the western part of the State, is near the village of Camillus in Onondaga 

 county, where folia of large size and nearly transparent have been found. With these spe- 

 cimens, both here and near the Split-rock quarry, the fibrous variety has also been obtained 

 of considerable beauty. The fibres, however, are coarse, and want the beautiful lustre of the 

 foreign specimens. Similar varieties are often met with in all the more extensive plaster beds 

 of the western counties. Sometimes also imperfect crystalline forms are observed. 



In the vicinity of Manlius, crystals are occasionally 

 found, having the form of the trapezienne of Haiiy. 

 Fig. 103. P on/ 124° 41' 43''; P on I 108° 3' 19"; 

 /on/ 110° 36' 34"; / on I 143° 53' 22". 



Niagara County. Fine specimens of selenite and 

 snowy gypsum have been obtained in considerable abun- 

 dance in the vicinity of Lockport. They occur in nodules 

 in the limestone, associated with the beautiful calcareous 

 and pearl spar and anhydrite. Snow-white granular gypsum also occurs in the same rock 

 near the Falls of Niagara, with occasional specimens of selenite. 



Schoharie County. Gypsum is deposited in very minute 

 crystals, from the waters of the Sharon sulphur spring. They 

 are white and transparent, and the usual form is similar to the 

 accompanying figure (104), the longer terminal edges of the 

 primary being replaced by new planes. 



Fig. 104. 



ANHYDRITE. 

 [From the Greek avWpoc;, in allusion to its being without water.] 



Chaux Anhydro-sulfatee. i7rtftv. — Anhydrous Sulphate of Lime. Cleaveland. — Prismatic Gypsum, or Anhy- 

 drite. Jameson. — Prismatiches Orthoklas-Haloid. Mohs. — Muriacite. Werner. — Karstenite. Bcudant. — 

 Anhydrite. Phillips, S/tcpard and Dana. 



Fig. 105. 



Description. Colour white, blue, red and grey. It is sometimes crystallized ; and when 

 its structure is foliated, it is easily cleavable into a right rectangular 

 prism, which is the primary form. Fig. 105. It also occurs in granu- 

 lar, fibrous, and lamellar concretions ; massive, and vermicularly con- 

 voluted or contorted. Fracture splintery and conchoidal. Lustre vitre- 

 ous, inclining to pearly. Varies from transparent to translucent on the 

 edges. Hardness from 3.0 to 3.5. Specific gravity from 2.70 to 

 to 3.00. Before the blowpipe, it behaves like the preceding species, 



except that it gives out no water ; and this, together with the difference in crystalline form, 



will sufficiently distinguish it. 



