610 MANUAL OF NATUEAL HISTOEY. 



silica and alumina as "Chrome ochre/' 

 clayey, greenish. Oxide of chromium colours 

 the emerald, and a variety of chrysoberl. 

 Chromic solutions are green or violet, with 

 borax a green glass is formed, becoming of a 

 deeper shade when cool. Symb. Cr. 

 11. Family. — Stypteriides. Minerals containing 

 compounds of Aluminium. Occur 1, as 

 Oxide, " Sapphire/' " Corundum/' or " Eme- 

 ry/' rhombohedral, sometimes massive, sp. 

 gr. 4, H. = 9, colour various, in crystalline 

 rocks, river beds, fee. ; 2, as Hydrous-oxide 

 or " Diaspore," trimetric, sp. gr. 3*4, H. = 6 

 -6 '5 ; grayish, very brittle ; 8, as Sulphate, 

 in combination with sulphates of other metals, 

 usually of potassa, soda, or magnesia, " Na- 

 tive alum/' octahedral, soluble, astringent ; 

 4, as Phosphate, with silica, calcia, copper, &c, 

 or " Turquois," reniform, stalactitic or en- 

 crusting, sp. gr. 2*6~2 , 8, H. =- 6, bluish-green, 

 in Persia ; 5, as Hydrous-Silicate m nume- 

 rous forms, as " Collyrite," " Halloysite," 

 " Allophane," " Finite," or combined with an 

 alkali, as the " Zeolites," which swell before 

 the blowpipe; 6, as Anhydrous -silicates, 

 also various, as " Kyanite," " Andulusite /' 

 with an alkali, forming the Felspars which oc- 

 cur in granite, gneiss, mica-slate, porphyry, 

 pumice, basalt, obsidian, &c. ; with silicates of 

 calcia, oxides of iron and manganese, dodeca- 

 hedral, or "Garnet," sp.gr. 3-5-4-3,H.=6-5-7'5, 



