Of all transparent substances, none can be compared to the
brilliancy of the diamond; and its hardness is such, that no kind of
steel instrument can make any impression upon it. Notwithstanding
which, it has been proved that the diamond is but carbon or
charcoal, in a pure or chrystallized state. When strongly heated,
it consumes entirely away. Diamonds, when rubbed together, have a
peculiarly, and scarcely to be described grating sound, which is
remarkably characteristic of this gem; so that by this circumstance
alone, rough diamonds may be accurately and expeditiously
distinguished from every other gem. When the diamond is rubbed,
it will attract bits of straw, feathers, hairs, and other small
objects, and if exposed to the rays of the sun, and immediately
taken into a dark place, will appear luminous.
The largest diamond ever known, is in the possession of the Queen of
Portugal, and weighs about eleven ounces. It was found in Brazil,
and sent from thence to London, in the year 1746. It is still uncut,
and has been valued at twenty-five million six hundred thousand
dollars.
Diamonds are much worn in England as ornaments. When converted into
powder or dust, the diamond is used with steel instruments to divide
pebbles and precious stones. Its use in cutting glass is generally
known. Rock crystal, brought from Brazil, is divided into leaves,
and ground and polished with diamond dust for spectacles, and other
optical instruments.