NON-METALLIC MINERALS. 
119 
the true zeolites in that it contains no alumina, being in fact a 
hydrous silicate of calcium and potassium. Especially note- 
worthy are the fine Indian crystals of apophyl'lite brought to 
light during the cutting of the railway tunnels on the stupen- 
dous inclines ascending the Bhore and Thul Ghauts, 
Case Y. — Zeolites. 
Here the visitor will find a large number of beautiful zeolitic 
minerals, which it is unnecessary to describe in detail. The 
differences in chemical composition are sufficiently explained by 
•the accompanying labels. Among the more noteworthy species 
attention may be called to natrolite, in beautiful needle-like 
crystals ; chabasite, in fine rhombohedral forms, almost like 
cubes ; harmotome, in milk-white twin-crystals, as though two 
individuals were crossing each other; and stilbite in crystals 
with broad cleavage planes exhibiting a pearly lustre. The 
salient characters of many of these species are sufficiently 
explained by their popular names, such as foliated zeolite, needle- 
-stone, radiated zeolite, effervescing zeolite, etc. 
Case Z. — Turquoise, &c. 
A few minerals containing phosphate of aluminium are 
grouped together in this, the last division of the Horseshoe Case. 
Childrenite is a phosphate of aluminium, iron, &c. found in a 
few localities only in Devon and Cornwall, and named after the 
late Mr. Children, of the British Museum. Wavellite is a 
mineral occurring chiefly in small globular concretions, which 
when broken present a beautifully radiated structure ; the 
species takes its name from Dr. Wavell, who discovered it at 
Barnstaple in Devon. Vivianite is a hydrous ferrous phosphate, 
which on exposure to the air becomes of a deep blue colour, and 
is not unfrequently found with phosphatic remains, such as 
fossil bones. Passing over a few other rare species, the visitor 
will be attracted by the specimens of Turquoise. This mineral 
is a hydrous phosphate of aluminium, containing copper ; and 
when of fine colour is valued as an ornamental stone. The 
finest specimens are found near Nishapur, in Persia, and some 
years ago discoveries were made in Arabia Petrsea. Ancient 
workings have of late years been re-opened at Los Cerillos, in 
Hew Mexico, where it occurs in a trachytic rock ; but much of the 
Mexican turquoise is of too greenish a tint. Some have supposed 
that this stone was the famous chalchikuitl of the ancient 
Mexicans. 
In addition to the true oriental turquoise described above, 
the jeweller avails himself of a substance somewhat similar in 
general appearance, but known as occidental turquoise. This is 
the odontolite of mineralogists, a substance which appears to be 
nothing more than fossily ivory, bone, or tooth, coloured with 
phosphate of iron. 
