SILICA. 



311 



That the composition of tliis mineral Joes notdiflcr essentially from that of some varieties 

 of pyroxene, and of metalloidal diallage, will be evident from the following statement : 



Pyroxene, by H. Rose. 



Silica, 54.08 



Lime, 23.47 



Magnesia, 11.49 



Proto.xidc of iron, 10.02 



Protoxide of manganese, 0.61 



MctalloiJal Diallage, by KniiLER. 



Silica, 51.34 



Lime, 18.28 



Magnesia, 15.(59 



Protoxide of iron and manganese, . 8.23 



Alumina, 4.39 



Water, 2.11 



The true Labrador liypersthene contains, it will be observed, a much smaller proportion of 

 lime (see page 310). 



The Waricickile of Shcpard, which closely resembles hypersthene in its external charac- 

 ters, has been found to contain a large proportion of titanium, and will be therefore described 

 under that metal. 



SCHILLER SPAR. 



[From the German, signifying chatoijant spar.] 



Schiller Spar. Thomson. — Sohiller Spar. Phillips and S/uyurrf. — Diallage. Horn/ and Clcavcland. — Diato- 

 mous Scliiller Spar. Jameson. — Diatomer Schiller Spar. Mohs. 



Description-. Colour dark green, almost blackish green. Streak yellowish grey. It occurs 

 in broad foliated masses, wiiich cleave in two directions, and apparently have the primary 

 form of a rhombohedron. One of the cleavages is easily obtained, and has a metallic pearly 

 lustre and a pinchbeck brown colour. The lamins are slightly curved. Fracture uneven, 

 splintery. Lustre metallic pearly on the faces of cleavage. Opaque, and yields to the knife. 

 Sectile. Hardness from 3.5 to 4.0. Specific gravity 3.65. Thin fragments, treated by the 

 blowpipe, are merely rounded on the edges, but become of the same brown colour as when 

 they have been long exposed to the air, and are attracted by the magnet ; with borax it is fu- 

 sible, though with difficulty, and the glass, when cold, has a greenish colour. 



Composition'. Silica 43.90, magnesia 25.86, protoxide of iron and chromium 13.02, pro- 

 toxide of manganese 0.53, lime 2.64, alumina 1.28, water 12.43 (Kdlder). 



Geological Situation. This mineral was generally supposed to be found in serpentine ; 

 but it appears, from the analysis of Kohler, that the stone in whicli it occurs is identical in 

 composition with that of the schiller spar. 



fusible by the blowpipe, and according to the analysis of Mr. H. Seybert, contains silica 52.17, lime 20.00, magnesia 11.33, 

 alumina 4.00, deutoxide of iron 10.73, water 1.00. Clcavdand's Mineralogy, Appendix. 



