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Ch. 12: Tourmaline
GEMS AND PRECIOUS STONES.
The turquois is much used by Orientals to ornament their daggers, harness, swords, and pipes. At one time there was much demand for these gems, both in London and Paris, fine ring stones fetching as much as £10 to £40 each. A perfect stone of the size of a shilling, and of good depth, was stated to hare been sold for £100, but there does not appear to be any fixed value for these gems.
The turquois is cut
on a leaden wheel and polished on a wooden one, and finished with rouge.
is a name given to the bone remains of extinct animals, these being coloured blue by phosphate of iron. They are brought from Siberia and have a striking resemblance, when cut, to the true turquois. They differ from it, however, by emitting an odour when gently heated, and besides the organic structure is easily detected by the aid of a microscope. "When the true turquois is dissolved in hydrochloric acid, and ammonia added in excess, a blue coloured liquid results, showing the presence of copper. The bone turquois being coloured by iron does not give a blue colour when thus treated. Theophrastus mentions a fossil ivory having variegated colours of white and blue which was largely used by the jewellers of his time.
Turquois is rarely found in Australia; fairly good specimens have, however, been found at Hedi, King River, Victoria. The turquois from this locality exists with or without quartz in veins running through a slate rock. The colour of some portions is fairly good, but the veins are often very thin. I have not been able to ascertain whether stones cut from this turquois retain their colour, but a specimen from this locality which has been in the Museum collection for a few years appears to have perfectly retained its colour.
During the year 1891 a discovery of turquois was made on Mount Lorigan, in the Wagonga Division, Southern Miring District of New South Wales. At present little information is obtainable as to the value of the find.
Cyrstalline system—Hexagonal, usually in striated prisms, with the crystals differently terminated at opposite ends.
Specific gravity—2'9—3 3.
Composition—Very variable and complex. All contain silicate of alumina, with boracic acid up to 10 per cent., iron, magnesia, lime, and soda, and from 1 to 2 per cent, of fluorine. Traces of phosphoric acid are usually found, and sometimes lithia.
As usually seen in New South Wales, the tourmaline is jet black and opaque, and is the variety
a name thought to be derived from a village in Germany, and applied to this mineral by the miners of that locality. If all tourmalines were of this character, it would not be necessary to consider them here, because commercially this variety has no value.
When the tourmaline is red or pink, it is known as
and when transparent is cut as a gem. The indigo-blue tourmaline is
When of a Berlin-blue colour and transparent, it is cut as a gem, and is known commercially as
The red is
is green and transparent, and of all the varieties is most largely used as a gem. The honey-yellow is called
Peridot of Ceylon,
and the colourless specimens are known as
; so that the range of
Table Of Contents
Smith. Gems and Precious Stones.
Preface & Contents
: The Diamond
: Sapphires, Rubies
: Beryl: Emeralds, Aquamarine
: Semi-Precious Stones
: Forms of Cutting
: Buying and Selling
: Synthetic and Imitation Gems
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