620 MANUAL OF NATURAL HISTORY. 



green with minute red spots it is "Blood- 

 stone ;" silica is held in solution by the hot 

 waters of the Geysers ; quartz is distin- 

 guished by its hardness, infusibility, inso- 

 lubility, and uncleavability ; 2, as Hydrate, 

 or "Opal/' amorphous, H. = 5*5 — 6*5, sp. 

 gr. = 2 — 2*21, variously tinted, frequently 

 opalescent; 3, as Silicic acid, united with 

 bases, forming " Silicates/' Symb. Si. 

 3. Family. — Boronides. Minerals containing com- 

 pounds of Boron. Occur 1, with oxygen as 

 " Boracic acid/' in yellowish, pearly scales ; 

 H. = 1 ; sp. gr. = 1*48 ; whitish ; 2, united 

 with bases forming borates. Boracic acid 

 and borates, tinge flame green. Symb. B. 



VIII. ORDER.— OXYGENEXIDES. 



Minerals containing elementary substances of the 

 oxygen series. 



1. Family. — Oxygenides. Minerals containing prin- 



cipally compounds of oxygen. This the most 

 abundant element in nature seldom, if ever, 

 occurs pure. It unites with all the other 

 elementary bodies, except Fluorine, forming 

 oxides, which act the part of bases ; mecha- 

 nically mixed with Nitrogen it is atmospheric 

 air, of which it composes one-fifth ; with Hy- 

 drogen it forms water sp. gr. - 1*1026, 

 colourless, supports combustion. Symb. 0. 



2. Family. — Theionides. Minerals containing Sul- 



phur, either pure, or in combination. Occur 



