frequently
mixed with a Tariety of other stones, and the places where it is found
are so numerous, that only a few of the most important can be mentioned.
In
Hindustan, garnet is abundant in the debris of mountains; and in Ceylon
it occurs everywhere in gneiss, particularly at Trincomalee and at Adam
s Peak
The
jacinth, sometimes called hyacinth, is an orange-red variety, it
differs in some respects in character from the deep red garnets, and is
considered by lapidaries as a distinct stone. This is a mistake, as its
crystalline form and typical composition are identical with that of the
other garnets. Its chief difference, besides its peculiar colour, is a
lower specific gravity, and the presence of 30 per cent of line in lieu
of protoxide of iron. The specific gravity is 3*65; It is known to
mineralogists as the essonite or cinnamon stone.
Jacinth,
or cinnamon stone, comes almost entirely from Ceylon, where it is found
in large pieces in the strata of rocky mountains ; these stones are
generally fiaely coloured and transparent. They are cut thin on account
of the depth of colour, with a pavilion-cut below and a broad ta,ble
above, bordered with small facets.
Rock
crystals are found in a variety of forms, sometimes of extraordinary
size. Their colour varies from pure white to greyish-white,
yellow-white, yellowish brown, clove-brown, and black. They possess
double refraction and transparency; The electricity obtained by
friction lasts about half-an-hour, rarely longer except under very
favourable conditions. Before the blow-pipe many coloured crystals lose
their tints. The frequent admixture of chlorite, asbestos, rutile, iron
pyrites( gold, and radiolite in the crystals is very
remarkable. The green colour of the last is like a blade of grass
inclosed in ice. The liquid or gaseous contents) which move as you turn
the crystal, are very interesting.
Ceylon affords it adbundantly, and the natives use it for ornamenting their temples.
The Tourmaline.
Tourmaline,
known in Saxony as " Schorl," from the name of a village where it
abounds, is mainly composed of alumina, silica, and boracic acidj
although there are specimens which contain a small quantity of iron and
manganese; The crystallization is rhomboidal; its cleavage is
imperfect, and its fracture conchqidal. It is very brittle. Its
hardness is 7 to 7'5, and its specific gravity 29 to 3-2. Tourmaline is
rarely found of pure-water. Its colours are very-Varied, consisting of
shades of greys, yellows, greens, blues, and browns; they all have a
tendency towards the darker hues, even to black. A black or red kernel
is not infrequently found in the midst of the stone.
Tourmaline
possesses double refraction. Some specimens polarize light perfectly,
and by the aid of the polariscope it is easy to detect the pure gem
from the yellow and green specimens.
Tourmaline,
in common with other precious stones, developes electricity under
friction, and is a mineral of the greatest interest from a
thermo-electric point of view. Its dust is attracted by the magnet.
The Dutch introduced tourmaline, somewhat more than a century ago, into Europe from Ceylon.
The
yellowish-green tourmaline (Ceylon chrysolite) is very like
aquamarine, and is found in the river-beds of Ceylon and Brazil.
Colourless tour; maline occurs very seldom in pieces worth the cutting
and polishing. The most beautiful specimens are found in Elba and in
dolomite mountains. Brown tourmaline is a variety not used for
ornament. Ceylon and Switzerland yield a fair supply.
The
value of the tourmaline depends upon the colour, quality and size of
the specimens; one of exceptional colour and purity, of five carats
weight, would be worth £?o.
The Zircon, Jargon, or Hyacinth.
The
Zircon, jargon of lapidaries, and hyacinth, are all varieties of the
same stone. Its name in Greek is " Uakinthis," in Latin " Hyacinthus,"
in
