54 
EAST WING. 
General high refractive power, approaches even the diamond in bril- 
CoUectionof ^^^^^^^ 
Minerals. 
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). 
iN'ext comes the Amethyst (14h), one of the less valuable, though 
one of the most beautiful of the ornamental stones. The 
Quartz Cat's-eye (13f) is a variety presenting the opalescence, 
but not the hardness or the 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 crocidoKte in the blue, and of altered crocidolite in the 
brownish-yellow specimens from South Africa. 
Jasper (13g), an uncrystallised coloured mixture of silica and 
clay, is distinguished 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 the Egyptian J asper, at other times in stripes 
as in the Eiband Jasper. 
The Lydian- or Touch-stone (15a), by reason of its hardness 
and black colour, has been used from remote ages to test the 
purity of the precious metals. 
Hornstone (15a) is a variety of silica without evident crystal- 
lisation, and generally presents a more or less splintery fracture ; 
but in one kind, Flint (15b), the fracture is conchoidal, some- 
times conical, as is well shown by specimens in the case. 
Chalcedony (15b) has a lustre nearly that of wax, and is 
either transparent or translucent. The specimens from Uruguay 
(15d) are of especial interest as containing imprisoned water. 
The Heliotrope, or Bloodstone (16a), is a green stone with red 
blood-like spots. 
Next follow the Plasma and Chrysoprase, green stones : and 
the Sard, generally a brownish red ; as also the Sardonyx, its 
banded variety : all of them much prized by the ancients 
Ijecause, though hard and tough enough to resist ordinary wear 
and tear, they are more suited to the display of the engraver's 
skill than are the harder and more precious stones. 
