270 



DESCRIPTIVE MINERALOGY. 



TABULAR SPAR. 



Schaaletein. Ckaveland. — Spath en Tables, Wollastonite. Hany. — Wollastonite, or Prismatic Augite. Jarne- 

 soa. — Prismatischer Augit-Spath. Mohs. — Bisilicate of Lime. Thoms&n, (wlio describes a new Wollasto- 

 nite.) — Wollastonite. Bcudant. — Tabular Spar. Phillips, Shcpard and Dana. 



Description. Colour white, with a shade of grey, yellow, red or brown. It occurs in granu- 

 lar and lamellar concretions ; also massive and disseminated. The primary form is a right 



Fig. 184. 



(or oblique) rhombic prism. Fig. 184. M on M' 95° 20'. Principal 

 cleavages parallel to the planes of the primary. Fracture splintery. 

 Lustre pearly vitreous. Translucent to opaque. Brittle. Hardness 

 from 4.5 to 5.0. Specific gravity from 2.80 to 2.90. Before the 

 blowpipe, it melts with difficulty into a semi-transparent colourless 

 enamel ; with borax, it fuses easily into a transparent glass. It forms 

 a jelly with muriatic acid, and the solution, after the separation of the 

 silica, gives an abundant precipitate with carbonate of ammonia ; and 

 it may thus be distinguished Irom carbonate of lime, gypsum and 

 tremolite, each of which tabular spar sometimes resembles. 



Composition. The results of all the analyses that have been made of this mineral, concur 

 in showing that it is a bisilicate of lime, but it is never free from small quantities of foreign 

 matter. According to Stromeyer, it contains silica 51.45, hme 47.41, oxide of iron 0.40. 

 Formula Ca + 2Si0.v 



Geological Situation. It occurs in primitive limestone, in various parts of northern New- 

 York. 



LOCALITIES. 



Essex County. At Willsborough, nine miles northwest of Essex, this mineral forms the 

 sides of a powerful vein of garnet which traverses gneiss. It occurs in cleavablc masses, 

 white and translucent. A specimen from this locality was analyzed by Mr. Vanu.xem.* Its 

 composition was as follows : 



Silica, 51. 67 



Lime 47.00 



Oxide of iron, 1.35 



In the town of Lewis, about ten miles south of Keeseville, tabular spar is found in abun- 

 dance, with similar associates as at the last named locality. The garnet exhibits various 

 colours ; it is massive, and in grains, forming the variety called colophonite. The tabular spar 

 is very friable, and has a white or yellowish white colour. 



^ Journal of the Academy of Natural Scietices of Philadelphia. U. 162. 



