SILICATES. 
69 
transparent, tough, and elastic. One of these minerals, Musco- Silicates, 
vite (28d), has been used in Eussia in place of glass for win- 
dows ; it is now in common use for lanterns and stoves, not 
being so easily cracked as glass by change of temperature : it 
is often known in commerce as talc, a term now restricted by 
mineralogists to a different mineral. 
The group of Felspars, the most important of the rock-forming 
minerals, begins at case 28f. After the Felspars comes Beryl, 
of which the bright green variety, Emerald (29c), is one of the 
most valued of precious stones. It was in ancient times 
worked in Egypt, as is proved by the specimens found in the 
old workings by Sir Gardner Wilkinson, and presented by him 
to the Museum, Emeralds are found in the Urals ; but the 
locality for the finest stones has long been that of Muso, about 
seventy miles from Santa Fe de Bogota, in South America. 
Emeralds, though not of a good colour, also occur at Stony 
Point, North Carolina. Facetted specimens of the colourless 
beryl, and also of the bluish-green beryl, known in jewellery as 
Aquamarine, are exhibited (30a). 
In cases 30e to 32d will be found examples of the Zeolite 
group of minerals. 
Tourmaline (33a), when free from flaws, is, in some of its 
varieties, to be classed with the precious stones. Among these 
is the pink variety called Eubellite. Two fine specimens of 
rubellite from Ava are shown in the case ; one, remarkable for 
its size and shape, was brought from that country by Colonel 
Symes, to whom it had been presented by the king ; the other, 
not so large but of a deeper colour, was presented to the 
Museum by Mr. C. S. J. L. Guthrie. The pink-and-green 
tourmalines from Maine, U.S.A., are among the more beautiful 
of the mineral products of the United States. Examples of 
the blue tourmaline, Indicolite, are shown in case 33b. 
A rich blue mineral product, the Lapis Lazuli of jewellery 
(34b), is brought from Persia, China, Siberia, Bokhara, and 
Chili ; it is a mixture of various species. When powdered, 
lapis lazuli furnished the once costly pigment ultramarine ; 
l)ut 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. 
