while
the darker indigo blue stones are called Lynx Sapphire. Fine specimens
have been found at Haddam in Connecticut, in gneiss, associated with
Tourmaline. The gem must be cut with the large exposed face parallel to
the most perfect cleavage plane to bring out the best colour. It is
usually step cut or table cut, but a variety showing asterism is cut en cabochon; and
sometimes the mineral is cut in cubes, with the surfaces normal to the
three axes of the crystal, to show the pleochroism. Its low specific
gravity is usually sufficient to distinguish it from other blue stones,
but in addition the strong pleochroism is of aid.
365. Lapis Lazuli.
Lapis
Lazuli is only to be regarded as a mineral in so far as its beautiful
colour, on which its use as a precious stone depends, is due to the
presence of a disseminated mineral in a matrix. The term Lapis Lazuli
thus refers rather to a rock, and the colouring mineral is now more
often known scientifically as Lazurite. Nor is Lazurite the only
coloured mineral present, for it has been shown that two other blue
minerals, Hauyne and Sodalite, may also be in the matrix, as well as
several substances whose colour does not affect the whole so much.
Lapis Lazuli, which is also known as Azure Stone, was almost certainly
the Sapphirus of Theophrastus and other ancient writers. It has been
known from very remote times, being much used by the Egyptians, and to
a lesser extent by the Assyrians. Epiphanius, Bishop of Salamis, says
the Tables of the Law given to Moses were inscribed on Lapis Lazuli.
The Romans used it to some extent as a material for engraving on.
