56 
NORTH GALLERY. 
[upper 
Div. lY. silicate ; Fayalite, di-ferrous silicate ; with Olivine and Hyalosiderite, 
the magnesio -ferrous silicates of the series. Chrysolite is the 
name of the pale yellow gem into which the larger and clearer 
specimens of Olivine are occasionally cut ; while the Peridot is a 
pistachio-green variety, of which fine crystals and cut specimens are 
exhibited in Case 36. Gadoliuite is di-yttrious silicate (containing 
also cerium, &c.) ; and Hamite, a mineral containing Fluorine, 
belongs also to the more basic silicates. 
Cases 36 Among the mono-silicates are arranged the large series of im- 
(ii.)to38. portant minerals which form the two parallel groups of the Augitesi 
and the Hornblendes. In juxtaposition with these is seen Wollas- 
CaseSS (ii.) tonite, the calcium motiosilicate, and the anorthic minerals Rhodonite 
and Babingtonite, homotypic in composition, but crystallographically 
differing from the other members of the series. The Augitic and 
Hornblendic groups present two distinct crystallographic types. In 
Case36 (ii.) Enstatite, the magnesian, as in Bronzite a magnesio-ferrous mono- 
silicate crystallises in the orthorhombic system, though with certain of 
the angles of an Augite ; while in Diopside, and the other Augites, 
clinorhombic in crystallisation, part of the Magnesium is displaced by 
Case 38 (i.) Calcium, and also by Iron, Manganese, or Zinc. So Anthophyllite, a 
magnesio-ferrous monosilicate, corresponding with Bronzite, presents 
orthorhombic forms with angles belonging to the type of the Horn- 
blendes, as exemplified in Tremolite and the other members of the 
Case 38 (ii.) group, which, however, crystallise in the oblique system. Certain 
varieties of Jade or Nephrite are assigned to these groups, as are also 
different kinds of Asbestos. 
Cases 39 The hydrated section of this series contains the Serpentines and the 
talcose minerals. It comprises, also, Dioptase and Chrysocolla, hy- 
Case40(ii.) (jj.g^(^g(j cupric mono-silicate; Hemimorphite, the hydrated zinc sili- 
cate and Apophyllite, a hydrated potassio-calcium silicate, extra- 
ordinarily fine specimens of which are seen in Case 39, and in the 
glazed fronts of Cases 11 and 12. 
The second series in the class of the silicates consists of those of the 
" sesqui-oxides." Foremost among them is the Topaz, an aluminium 
silicate, in which part of the silicate is replaced by an analogous 
Case 41 (i.) fluosilicate. The specimens of this mineral from the Ourulga 
river in Siberia, collected by Col. de Kokscharow, are singularly fine. 
They are of a delicate sherry-colour, but are preserved in the dark, 
as light speedily bleaches them. 
The third series of the silicates is constituted of those in which the 
monoxides and sesqui-oxides are associated in the same mineral. 
The various groups known by the general names of the Garnets, 
Scapolites, Idocrase, Epidote, the Felspars, the Micas, and Dichroite 
(with a variety of minerals resulting from its alteration) find their 
places in this series, into the hydrated section of which fall the beauti- 
ful and extensive varieties of Zeolites and Chlorites. 
Ca.'ie 42. Among these the Garnets form a group of minerals belonging to the 
cubic system in which the chemical type j (m''o)JM''\0.j ( SiOg] I 
