or, as they are commonly called, rough, by the evident action of fire, which Nature uses in forming them.
It breaks regularly into four principal cleavages.
Eeduced
to powder, it still preserves its prodigious hardness ; and though it
may appear that this quality might prevent its pulverization, yet it
must be remembered that the hardness of a body does not generally
prevent its being reduced into minute particles.
This
mineral becomes electrical and phosphorescent. It acquires the first
property by friction, but only preserves it fifteen or twenty seconds.
Its
phosphorescent property is apparent not only in a strong light, but
when shaded by glass, paper or muslin, and even covered by a sheep's
skin, and behind a table of linden wood of the thickness of two hundred
millimetres. In order to deprive it of phosphorescence, it must be
wrapped in black or dark coloured paper.
The specific gravity of the diamond varies from 3-444 to 3'550, that is—
