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CHAPTER XI.
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BORT.
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ERTAIN
Diamonds are found of inferior quality, and so imperfectly
crystallized, that they are useless as ornamental stones. These are
called " Bort," or " Boort," and are either crushed to form Diamond
dust, or are used for engraving. By mineralogists the name Bort is
restricted to a form of Diamond, which generally presents the
appearance of small nodules or spherical masses, rough on the outside,
and destitute of cleavage, but displaying on fracture a radiated
internal structure. It is usually greyish white, or of a dark or even
black colour, and has a density a trifle less, but a hardness decidedly
higher, than that of ordinary Diamond. Under the microscope it shows a
confusedly crystalline structure.
The
best kind of Bort, the round, is now used as an abrasive in
rock-boring, and when suitable fetches even a higher price than the
cutable Diamond, the supply not being equal to the demand. Much Bort,
too, is crushed in steel mortars and used in the form of powder. This
powder, as well as that which is the produce of the operations of
cutting and cleaving rough stones, is after mixture with oil, employed
for polishing Diamonds, Rubies, Sapphires, and other gems.
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