SULPHATES AND PHOSPHATES. 
93 
lazuli furnished the once costly pigment ultramarine ; but 
by the discovery of a method of producing an artificial and 
cheap form of the latter, the use of the mineral as a pigment 
has almost ceased. 
The sulphates of strontium, Celestite (35c), of barium, Barytes Sulphates, 
or Heavy Spar (36a), and of lead, Anglesite (36e), are all repre- et^°^^^^^^' 
sented by series of specimens. 
Gypsum, or Selenite (36f), is a sulphate of the metal calcium: 
when heated, it gives up its water of crystallisation and falls to 
a white powder, known as "Plaster of Paris," which, when 
moistened, 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), a borate of sodium, is much used as a flux, also 
in soldering, and in the preparation of easily fusible enamels. 
It was formerly carried over the Himalaya on sheep and 
goats from a lake in Tibet, but is now obtained largely from 
the borax-lakes of the United States, and is also extensively 
prepared from the boracic acid lagoons in Tuscany. 
Nitratine or Soda-nitre (37d), found in Chili in beds of large 
extent, is largely used for the preparation of nitric acid and of 
saltpetre, and also as a fertiliser. 
Calaite or Turquoise (38g), a phosphate of the metals alu- 
minium and copper, does not occur in the crystalline state. 
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 being chiefly 
brought from the turquoise-mines not far from Mshapur, 
in Persia. 
As a supplement to the collection of simple minerals, is 
arranged, in case 41, a group of natural substances which 
either belong or are closely related to the Mineral Kingdom, 
although, in the formation of most, 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 
