(1) Turquois matrix consists of bits of turquois in a limonite matrix.
Odontolite—it is not real turquois, but is bone fossil turquois. It is
coloured blue either artificially or naturally distinguished by its
is formed from solutions, its associate being limonite, quartz,
felspar, etc. Good turquois comes from Persia and Egypt. In India it is
found in the Ajmer hills and at Ramgarh, Rajputana.
is another hydrated aluminium phosphate of an apple-green colour which
is caused by the presence of chromium and vanadium. It is used at times
in place of turquois.
LAPIS LAZULI (LAZURITE)
has been known from very ancient times, as it was used for mosaics,
inlaid work, etc., and was also used for the pigment ultramarine. It is
a mixture of a number of minerals, of which lazurite is the most
important, as it imparts the blue colour. Other minerals present are
hauyne, diopside, amphibole, calcite and pyrite. Hardness = 5-1/2.
Specific gravity varies from 2-5 to 2-95. Sp. gr. of the pure mineral
is 2-4. Colour varies from deep blue to azure blue, etc. Lustre:
Vitreous to greasy. Opaque to transparent. Cubic. Refractive index =
1-50. It has a complex chemical composition. It is a complex
alumino-silicate and sulphide of sodium accompanied by HC1.