70 
MINERAL GALLERY. 
Sulphates, The sulphates of strontium, Celestite (35c), of barium, Barytes 
Phosphates, -RediYj Spar (36a), and of lead, Anglesite (36e), all repre- 
sented by series of specimens. 
Gypsum, or Selenite (36f ), is the hydrated sulphate of calcium: 
when heated it gives up its water of crystallisation and falls to a 
white powder, known as " Plaster of Paris " ; when moistened 
the powder again combines with water and yields a coherent 
solid. Gypseous alabaster, a massive variety of gypsum (36h), 
owing to its whiteness, fine texture, and softness, is used as a 
material for statuettes and other indoor ornaments. Oriental 
alabaster is a harder substance, stalagmitic calcite, the carbonate 
of calcium. 
Borax (37c) is a hydrated borate of sodium. It is much used 
as a flux, also in soldering, and in the preparation of easily 
fusible enamels. It was formerly carried over the Himalayas 
from a lake in Tibet, but is now obtained largely from borax- 
lakes of the United States, and is also extensively prepared 
from the boracic acid of the lagoons in Tuscany. 
Mtratine or Soda nitre (37d) is found in Chili in beds of 
large extent; it is largely used for the preparation of nitric 
acid and of saltpetre, and also as a fertiliser. 
Calaite or Turquoise (38g) is a hydrated phosphate of alumi- 
nium, which owes its blue or green colour to the presence of 
small quantities of salts of copper and iron. Being as hard as 
felspar and taking a good polish, it has been much prized in 
jewellery under the name of Oriental Turquoise; that which 
comes into the market is chiefly brought from the turquoise 
mines, not far from Mshapur, in Persia. 
• As a supplement to the collection of simple minerals, there is 
arranged, in case 41, a group of natural substances which 
either belong or are closely related to the Mineral Kingdom, 
although in their formation organised matter has played a very 
important part. The most important members are Coal and 
Amber. Coal (41a), in most of its varieties, gives structural 
evidence of its vegetable origin : its chemical composition 
depends on the amount of change which has taken place, and is 
thus not so definite as in the preceding minerals. In the 
variety called anthracite all traces of the original organised 
structure have disappeared. Amber (41c), in ancient times 
