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a half. He had about 108 more rubies in his throne, from 100 to 200 carats each, before the invasion of Nadir Shah, or Couli Khan. Russia has as yet discovered no rubies in Siberia, which produces so many other gems.

Value and Rarity.

A ruby of one carat, is worth ten guineas; one. of two carats, forty guineas, one of three carats, 150 guineas; and those of six carats above 1000 guineas. N. B. A ruby above three carats is worth more than a diamond of the same weight. Ballas worth 3s. per carat. Spinel, half as much as a diamond.

Clafs third.

SAPPHIRE.

The SAPPHIRUS of the ancients.

HARDNESS from 17 to 16; SPECIFIC GRAVITY from 4,7 to 3,8. Varieties.

DEEP BLUE, PALE BLUE, and MILKY BLUE

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The sapphire is commonly in two oblong hexagon pyramids, joined at their base, and pointed at top; sometimes also in hexagonal columns.

* Bergman,

Structure, Properties, &c.

Texture laminar. Electric on friction. The orien tal does not lose its colour in the fire, like the softer and inferior sorts; nay, even those of Puy, inAuvergne, and of the Brazils, although in every other respect of hardness, form, and specific gravity, they equal the oriental, do not preserve their colour in the fire. It does not melt per se, but is affected by the same fluxes as the ruby. The sapphire is preferable to the ruby for jewelling clock work, from its equal hardness, a quality not to be found with certainty in most of the other varieties except the oriental. Largest.

Authors make mention of no remarkable sapphire either for size or value, except one belonging to the king of France, with a strip of fine yellow topaz in the middle. This is another proof of Rome de Lisle's hypothesis mentioned in the article ruby.

Where found.

The finest sapphires, like most of the gems, come from the East Indies. Rufsia does not produce the: sapphire. In Scotland, they are found of a hardnefs and lustre equal to the oriental, both light and deep. coloured, at Benachie, and Invercauld, Aberdeen-. fhire, Portsoy in Banffshire, and many other places. Mr Deuchar, seal engraver in Edinburgh, has in his pofsefsion, a beautiful sapphire, which was found in a double crystal. On one of these is cut a head, which was effected with the greatest difficulty, on. account of its hardness; the other is cut into facets, and has a fine water, and great brilliancy.

How valued.

A fine sapphire of ten carats, L. 50. One of twenty, L.200.

Under ten carats it may be valued by multiplying the carat at 10s. 6d. into the square of its > weight.

Clafs fourth.

TOPAZ.

The CHRYSOLITHUS of the ancients, according to Pliny,

HARDNESS from 15 to F1 SPECIFIC GRAVITY 4,2 to 2,8.

Varieties.

GOLD COLOUR, ORANGE, YELLOW, PALE YELLOW, WHITE and SMOKY.

Analysis.

*YELLOW SAFFRON, H 15; SpGr 4,2; Arg 41; Sil 21; Cal 20; Ir 18*.^

* WHITISH, H 14; Sp Gr 3,5.

BOHEMIAN, H 11; Sp Gr 2,8.

SAXON TOPAZ, Sp Gr 4,2; Arg 46; Sil 39; Cal 8; Ir 6 †.

Form.

The topaz is commonly in prisms of six or eight sides; or in parallelopipedal or cubic forms; some-times striated. They are terminated by two tetrapedal pyramids with smooth triangular faces.

Structure, Properties, &c.

The texture is laminar. Electric on friction. The occidental are said to lose their colour in the fire; and the Brazil topaz to acquire a fine ruby colour, as mentioned in the article ruby.. It does not melt per se; but borax and microcosmic salt promote its fusion.

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Where found.

They are found in India, Pegu, Ceylon, Arabia, Égypt, and Brazil. These are said to equal the ru by and sapphire in every respect; and differ from them only in colour. Occidental are found in Saxony and Siberia, as hard as the oriental; in Bohemia, Scotland, &c. Rufsia produces a variety; but the best are found in the mountain Adunfhollo, near the river Onon, in Dauria; particularly the remarkable hard quadrangular species,-certainly one of the best in Europe. It is distinguished among the Rufsian stones in having the sides of the prisms polished like glafs, and presenting, in some cut specimens, the appearance and texture of the Aventurine. As it merits to be analysed, the author has sent a fine prism to an able philosopher for that purpose. In Scotland the topaz is found in Strathspey, and In-vercauld Aberdeenshire; Caringoram, isle of Arran, Butefhire, o.

Largest.

The largest rough one is in the possession of the prince of Orange. It is an oval oriental topaz, seven inches long. Cut,-the Great Mogul pofsefses one of 157 carats; and a jeweller in St Petersburg, one of a square form, two inches and a half, by two and one third thick.

How valued.

The oriental topaz is valued by multiplying the square of its weight by fifteen or sixteen fhillings. The occidental by five or six fhillings.

Class fifth.

THE HYACINTH.

HARDNESS 15; SPECIFIC GRAVITY 2,8:

Varieties.

YELLOWISH RED, CHRYSOLETRE, AMBER COLOUR, ORANGE ORIENTAL, WHITE.

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ORANGE ORIENTAL, Sp Gr 2,8: Arg 40; Sil 25; Cal 20; Ir13*. WHITE cruciform Saxon, Arg 20; Sil 44; Bar 2,4 †.

Form.

The form of the hyacinth is commonly that of a prism, with five, six, seven, or eight sides, pointed at both ends, with four facets; but sometimes it is found in the globular polygon form of the garnet, only with its angles more obtuse. There are two sorts of gems sold by jewellers as hyacinths; the

first is the true one, very hard and brilliant, which seems only a variety of the topaz, higher coloured, or more loaded with iron, as their analysis demonstrates. The other a garnet of the hyacinth colour, but inferior in lustre and hardness.

Structure, Properties, &c.

The texture is laminar. Electric on friction. It either becomes paler, or loses its colour altogether, in the fire. Melts per se in a wind furnace in two hours, according to Mr Achard. The spurious hya

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