SULPHATES, PHOSPHATES, ETC. 
89 
lapis lazuli furnished tlie 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 (3Ga), and of lead, Anglesite (36e), are all repre- l^^i^osphatei 
sented by series of specimens. 
Gypsum, or Solenite (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 alu- 
minium and cop})er. It docs 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 is chiefly 
brought from the turquoise mines not far from Nishapur, 
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 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 
