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82 PRECIOUS STONES.
Nearly
all the iron was in the form of ferions oxide. The hardness of this
variety of garnet is about 7'5, while its specific gravity is seldom
less than 4'1 and may be as high as 4·3
3.
Pyrope or Bohemian Garnet.—The Pyrope is essentially a magnesium iron
aluminium garnet, but variable, and sometimes not inconsiderable,
quantities of other metals are present, so that this variety of garnet
must be regarded as belonging to a mixed type. Its colour is usually
blood-red, or deep red with some orange. It is usuallv perfectly
flawless and transparent, and, when of any size may appear of so dark a
colour as to be almost black. It is this blackness which is the chief
distinguishing feature between a blood-red pyrope and a blood-red ruby,
though the superior lustre, fire and dichroism of the latter gem afford
other criteria in the discrimination of the two stones. Moreover, in
hardness and in specific gravity the pyrope is inferior to the ruby.
This stone, which is found in great abundance, though of small size, in
many places in Bohemia, is usually rose-cut and often foiled. Specimens
from other localities, such as those from South Africa (often wrongly
called Cape rubies) are not infrequently brilliant-cut. The hardness of
pyrope lies between 7-1/4 and 7-1/2 ; its. density is just below 3-8, on the average about 3'75 It is less easily fused than any other garnet save uvarovite.
Three
analyses of pyrope are here given, as it is well to have this means of
comparing the percentage composition of this garnet from different
localities, and its divergence from almandine :
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These analyses cannot be discussed- here, but this at least may
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