OXIDES. 
65 
the colourless variety known to jewellers as the Lux-sapphire : Oxides, 
but with minute traces of colouring ingredient it assumes 
the richest and most varied hues ; when red it is Euby, 
when azure Sapphire, while the yellow, green, and purple 
varieties are known respectively to jewellers as the Oriental 
Topaz, Emerald, and Amethyst ; the prefix oriental," though 
at first used to suggest that the stones are not the ordinary topaz, 
emerald, and amethyst, but others of a similar colour coming 
from the East (India, Ceylon, Siam, Pegu, &c.), was afterwards 
understood to imply only the excellence of their characters. The 
Star-stone, another variety of corundum, when placed in a 
strong light shows a six-rayed star. 
Hsematite (11a) is a valuable ore of iron. 
Cassiterite, or Tin-stone (llf), is the ore of tin, of which metal 
it contains 79 per cent. 
Zircon (13b), when clear and without flaws, is one of the 
precious stones : one variety with peculiar red tints is the 
Hyacinth or Jacynth, while the colourless, yellowish, and dull 
green are termed Jargoon : the colourless variety, owing to its 
high refractive power, approaches the diamond in brilliancy. 
Quartz is the most common of minerals. In its clear and 
transparent variety it is the Crystal of the ancients and the 
rock-crystal of modern times ; it is the Brazilian Pebble of the 
spectacle-makers (14b). After the clear come the smoky varie- 
ties, including the Scotch Cairngorm and Occidental Topaz (14g). 
Next comes the Amethyst (14h), one of the less valuable, though 
one of the most beautiful of ornamental stones. The Quartz 
Cat's-eye (13f) is a variety presenting the opalescence, although 
not the hardness or brilliancy, of the true Cat's-eye already 
referred to : the opalescence is due to enclosed fibres of an 
asbestos-like mineral in the specimens from Ceylon, and to 
fibres of crocidolite in the blue, and of altered crocidolite in the 
brownish-yellow specimens from South Africa. 
Jasper (13g) is a coloured mixture of silica and clay, dis- 
tinguished from ordinary quartz by its opacity and dull earthy 
, fracture. It is of various colours, chiefly red, brown, yellow 
' and green ; and the colours are arranged sometimes in a 
nodular form as in Egyptian Jasper, at other times in stripes 
as in lUband Jasper. 
F 
i 
