loo THE PROSPECTOR'S HANDBOOK. 



schist consists of fine layers of quartz and chlorite ; horn- 

 blende schist consists of fine layers of quartz and hornblende. 



Jf.B. In the to-called igneous rocks sometimes the minerals are 

 distinctly crystallized, sometimes of a very compact appearance like 

 broken porcelain. 



Gneiss. 



Is made up of the same minerals as granite, only con- 

 taining them in parallel layers. 



Serpentine. 



A greenish, grey, brown, &c., mineral, opaque and trans- 

 lucent. Breaks with a conchoidal fracture. H. 2'25 to 4 ; 

 S.G. 2'5 to 2-6. Massive, foliated, or fibrous, and in 

 appearance pearly, resinous, or waxy. Before B.F. whitens 

 and gives off water. Contains 40 to 44 per cent, of mag- 

 nesia, 40 per cent, silica. 



Basalt. 



When broken, of a black, bluish, greenish, greyish brown. 

 &c., colour, though usually pale drab colour on the surface. 



Thin sections under the microscope show lath-shaped 

 crystals of felspar (not potash felspar) and augite, with 

 sometimes olivine, &c. 



Diorite. 



A crystalline rock made up of felspar (lime felspar or 

 lime-soda felspar) and hornblende or dark-coloured mica. 



Andesite. 



A volcanic rock with felspar (not potash-felspar) and 

 augite or hornblende or mica occurring in a non-crystalline 

 base. The crystals of felspar are frequently very glassy. 



Obsidian. 



A glass-like volcanic rock. It is often like dark bottle 

 glass in appearance and transparency. 



Pitchstone. 



A volcanic rock much resembling obsidian in certain 

 characteristics ; but has not transparency, and is more pitch- 

 like or resinous in appearance. Usually blackish ; some- 

 times, however, reddish-brown, greenish, &c. 



