50 
NORTH GALLERY. 
[UPPER 
Case38(ii.) 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 
and 40. the talcose minerals. It comprises, also, Dioptase and Chrysocolla, 
Case40(ii.) silicates of Copper ; Smithsonite, the silicate of Zinc; and Apophyllite, 
a hydrated calcio-potassic silicate, extraordinarily fine specimens of 
Case 39 (i.) which are seen in Case 39, and in the glazed fronts of Cases 11 and 12. 
The second series in this class contains the silicates of the epi- 
deufeoxides (sesqui-oxides). Foremost among them is the Topaz, a 
silicate of Aluminium, in which part of the silicate is displaced by an 
Case 41 (i.) analogous fluosilicate. The specimens of this mineral from the 
Ourulga river in Siberia, collected by Col. de Kokscharow, are singu- 
larly fine. They are of a delicate sherry- colour, but are preserved in 
the dark, as otherwise the light would speedily bleach them. 
The third series of the silicates is constituted of those in which the 
monoxides and epideutoxides are associated in the same mineral. 
The various groups known by the general names of the Garnets, 
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 beautiful and 
extensive varieties of Zeolites and Chlorites. 
Case 42. The Garnet group, a series of minerals in which the type alone is 
constant, while the isomorphous metals it contains replace each other in 
unlimited variety, is the first important mineral in the third series. To 
it belong the violet-tinted Almandine, the yellow and hyacinthine 
Garnets known as Cinnamon-stone and Essonite, the rich blood-red 
Syriam Garnet, the Bohemian Garnet and Pyrope, varieties which, 
when cut en cabochon, or with a concavo-convex or only a convex form, 
are the Carbuncle of jewellery. Idocrase, a mineral with a smaller range 
of chemical variation than the Garnet, is represented by a series of crys- 
Case 42. tals (of pyramidal forms) of remarkable variety and perfection. Epidote 
is also well represented. The group of Felspars follows, among which 
Cases 43 will be found Labradorite, with its beautiful play of colours ; the 
and 44. Moonstone, a partially decomposed Orthoclase ; and a fine specimen of 
the Orthoclase called " Valencianite " from Mexico. Dichroite (the 
Case 43 (ii.) Sapphire d'Eau of jewellers), exhibits an intense blue when looked 
through in one direction, and pale yellow-brown colours when the light 
Case 4G (i.) traverses the crystal in other directions. The Beryl includes the 
Emerald and also the Aquamarine of the jewellers, and with Euclase 
occupies half of Case 46. It is a silicate of Aluminium and Glucinum, 
the Aluminium being in the Emerald apparently displaced to a minute 
amount by Chromium. Euclase is a mineral composed of the same 
elements, and containing a small quantity of water; the specimens of 
it from Siberia are of high interest. 
50. The silicates proper are succeeded, in Case 50, by minerals in which 
silicates are associated with boric-oxide or borates. Among these 
the Tourmalines present a rich assortment of valuable and beautiful 
specimens, conspicuous for crystals of Rubellite, from Siberia and 
Ava. These are succeeded, in Case 51, by a class of minerals of great 
mineralogical interest, containing some of the rarest of the elements, 
