334 



DESCRIPTIVE MINERALOGY. 



hexaedre of Haiiy, Fig. 301 ; the same witli the obtuse solid angles replaced by single planes, 

 unihinaire of Haiiy, Fig. 302, and Fig. 303. The twin crystal, Fig. 304, geminee ohliquangle 



Fig. 301. 



Fie. 302. 



Fig. 303. 



Fij. 304. 



M 



M 



of Haiiy, has also been observed at this locahty, although it is usually imperfect. M on M' 

 129° 30' ; M or M' on P 90° ; M on o 115° 18' ; M or M' on r 137° 58'. 



New-York County. Three and a half miles from the city, on the banks of the Hudson, 

 this mineral is found in mica slate. It has the form of short but very perfect rhombic prisms, 

 with the acute lateral edges replaced by tangent planes, and terminated by dihedral summits 

 (Fig. 303), and sometimes forming an imperfect cross.* 



Staurolite probably occurs also in the counties of Rockland and Westchester. I have found 

 it in bowlders of mica slate on the banks of the Hudson, at Nyack. These bowlders more 

 nearly resembled the rocks found in Westchester, than those of Rockland. 



This mineral has been observed in the mica slate in Massachusetts and Connecticut. 



FELDSPAR. 



[From the German Feldspath, fieldspar ; probably from its being often found loose on the surface 



of the ground.] 



Feldspar. Tiiomson, Shepard and Dana. — Prismatic Felspar, or Common Felspar. Jameson. 

 Feld-Spath. Mohs. — Orthosc. Bcudant. — Felspar. PhUlips. 



■ Ortliotomer 



Fig. 305. 



Description. Colour white, grey, green, blue, red and brown, 

 sometimes with a pearly opalescence. Streak greyish white. It 

 occurs regularly crystallized ; and also massive and disseminated. 

 The primary form is a doubly oblique prism. Fig. 305. M on T 

 120° 35' ; P on M 90° ; P on T 67° 15'. Cleavage parallel with P 

 and M perfect ; with T obscure, though sometimes easily obtained. 

 Fracture conchoidal, splintery, slaty and earthy. Lustre vitreous or 

 vitreo-pearly. From transparent to opaque. Brittle. Hardness 6.0. 

 Specific gravity from 2 . 39 to 2 . 58. Before the blowpipe, on char- 



" Pierce and Torrey. Cleaveland's Mineralogy. 



