760 Marvels of the Universe 
The numerous varieties of 
crystals are the result of 
wonderful natural laws which 
are so constant and invariable 
that almost all the many 
materials of which the earth is 
composed have been classified 
under six groups or systems as 
represented on page 758. The 
most precious of all gems, 
because the most beautiful 
and the hardest substance 
known, is the diamond. It 
has been proved to consist of 
AN EMERALD CRYSTAL. 
A magnificent specimen from the Natural History Museum, over an inch long, 
pure carbon, but the exact 
Soa Us eerie onsale, Filta manner of its production can- 
not be said to be fully ascer- 
tained. Mr. Gardner Williams, a great authority on diamonds, when asked as to his theory 
of their origin, replied: ‘““I have no theory. ... All that can be said is that in some un- 
known manner carbon, which existed deep down in the internal regions of the earth, was changed 
from its black and uninviting appearance to the most beautiful gem which ever saw the light 
of day.’ In addition to the diamonds formed at considerable depths in the earth, there are 
many known instances of diamonds in meteorites, some of which are exhibited in the mineral depart- 
ment of the Natural History Museum. 
The largest known diamond, which may be only a portion of a very much larger one, is the 
famous “‘ Cullinan.” Its weight before cutting was 3,025 carats, or, expressed in avoirdupois, 
1 lb. 5 0z. 14 drs.! It was found about twenty miles from Pretoria. 
Several beautiful gems, such as the white and the blue sapphires, topaz, ruby, the oriental 
amethyst and the oriental emerald, are derived from alumina—the principal element of clay. In 
a crystalline state it is remarkably hard and durable, and is known as corundum. 
Quartz, the commonest of 
all constituents of the rocks 
of the globe, is the chief 
constituent of many beautiful 
stones—rose quartz, common 
amethyst, common topaz, 
chalcedony, avanturine, helio- 
trope, plasma, onyx, sardonyx, 
opal, jasper, carnelian, cairn- 
gorm, moss agates, agates, 
chrysoprase, and many 
others. 
Tourmaline consists of alu- 
mina and silica. It assumes 
a great number of colours, 
and is of more value _ for 
its scientific services than 
The largest known Dianond weighed before cutting 3,025 carats, or | lb. 5 oz. for its ornamental purposes. 
14 drs. avoirdupois. It is shown in its untouched state. Opticians by its use can tell 
THE CULLINAN DIAMOND. 
