on. In composition it contains about 20
per cent. of water, about a third of its substance being phosphoric
acid, or phosphorus-pentoxide; sometimes nearly half of it is alumina,
with small quantities of iron in the form of variously coloured oxides,
with oxide of manganese. The great proportion of water, which it seems
to take up during formation, is mostly obtained in the cavities of
weathered and moisture-decomposing rocks. Its average formula may be
said to be Al_{2}O_{3}P_{2}O_{5} + 5H_{2}O, and sometimes Al_{2}O_{3}
FeOP_{2}O_{5} + 5H_{2}O. It must therefore follow that when the stone is
heated, this water will separate and be given off in steam, which is
found to be the case. The water comes off rapidly, the colour of the
stone altering meanwhile from its blue or blue-green to brown. If the
heat is continued sufficiently long, this brown will deepen to black,
while the flame is turned green. This is one of the tests for turquoise,
but as the stone is destroyed in the process, the experiment should be
made on a splinter from it.

This stone is of very ancient origin, and many old turquoise deposits,
now empty, have been discovered in various places. History records a
magnificent turquoise being offered in Russia for about L800 a few
centuries ago, which is a very high price for these comparatively common
stones.

Owing to the presence of phosphorus in bones, it is not uncommon to
find, in certain caves which have been the resort of wild animals, or
into which animals have fallen, that bones in time become subjected to
the oozing and moisture of their surroundings; alumina, as well as the
oxides of copper, manganese and iron, are often washed across and over
these bones lying on the cave floor, so that in time, this silt acts on
the substance of the bones, forming a variety of turquoise of exactly
the same composition as that just described, and of the same colour. So
that around the bones there eventually appears a beautiful turquoise
casing; the bone centre is also coloured like its casing, though not
entirely losing its bony characteristics, so that it really forms a kind
of ossified turquoise, surrounded by real turquoise, and this is called
the "bone turquoise" or "odontolite."

INDEX

Adamantine lustre, 28
glimmering, 29
glinting, or glistening, 29
lustreless, 29
shining, 29
splendent, 29

Agate, 11

Almandine, 101

Amethyst, 11
oriental, 85
sapphire, 85

Amorphous stone