I 



SILICA. 281 



Two miles north of Rye, is another and more abundant locahty of the same mineral. It 

 usually occurs in thin and very brittle plates of a white or light green colour. It has a some- 

 what resinous lustre, and is translucent on thin edges. Sometimes, however, it appears to 

 be largely intermixed with true serpentine, and forms masses of considerable size. These 

 masses are usually made up of angular fragments, separated from each other by thin seams 

 of hydrate and carbonate of magnesia, the hydrate being in small pearly imperfect crystals 

 or plates, and the carbonate in a white powder, probably resulting from the action of the 

 atmosphere upon the hydrate. 



According to my analysis of the green and compact portion, it contains 



Silica, 40.50 



Magnesia, 38 . 00 



Water, 21.00 



Oxide of iron, traces. 



This mineral, therefore, is quite similar in composition to that from Staten island. 



The so called Agalmatolite, from Warwick in Orange county, is probably identical with 

 this species ; while the Pseudolite, (or the pseudomorphs, as they have been called, of horn- 

 blende, scapolite and spinelle,) which is supposed to belong to kerolite or magnesite, includes 

 several mixtures of the minerals whose crystalline forms they represent, and some of the mine- 

 ral matters which serpentine and magnesite are usually found to contain. 



The general similarity in the chemical composition of the several minerals just noticed, 

 sufficiently indicates their identity. The diflferences in some of the external characters may 

 easily be accounted for, when we reflect upon the usual associates of these minerals, and the 

 ease with which these associates are at least partly decomposed. Perhaps the most widely 

 different variety is that of a dark green colour found at Stony point, and which uniformly 

 contains from ten to twelve per cent, of oxide of iron. If I were to suggest a name for this- 

 mineral, it would be that of Rocklandite. 



CHONDRODITE. 



[From the Greek xov5pos, a grain ; in allusion to its mode of occurrence.] 



Chondxodite. Berzelius and T^unnson. — Brucite. Giibs, Cleavehmd and Shepard, — Condrodite. Haiiy, Phil- 

 lips and Beudard. — Hemiprismatic Chrysolite. Jameson, — Hemiprismatischer Chrysolith. Mohs. — Maclu- 

 rite. Seybert. 



Fig. 190. 



MiN. — Part II. 



Description. Colour various shades of yellow, brown and red. 

 It occurs massive and in small grains. According to Haiiy, it 

 cleaves parallel to the faces of a right oblique prism (Fig. 190), 

 the greater angle of which is 112° 12'; but Cleaveland describes 

 it as occurring in rhombic prisms of 124° and 56°, with dihedral 

 terminations. Fracture imperfectly conchoidal. Lustre vitreous 

 to resinous. Translucent. Hardness 6,5. Specific gravity from 

 36 



