748
LAPIDARY.
wood, according to circumstances; and the other c for receiving the upper part of thearbor of the large pulley d. The upper pulley of the wheel plate is supported by an if° nprop k, fixed to the table by two wooden screws. • The inferior pivots of the two pie ceSare supported by screw-sockets, working in an iron screw-nut sunk into the summer-ba^f. The legs of the table are made longer or shorter, according as the workman choosesto stand or sit at his employment. Emery with oil is used for grinding down, and tnj'putty or colcothar for polishing. The workman lays the piece on the flat of the wheel-plate with one hand, and presses it down with a lump of cork, while he turns round th ehandle with the other hand.
The Sapphire , Ruby, Oriental Amethyst, Oriental Emerald, and Oriental Topaz, a,egems next in value and hardness to diamond ; and they all consist of nearly pure alum inaor clay, with a minute portion of iron as the coloring matter. The following analy$ e ^show the affinity in composition of the most precious bodies with others in little relaU'estimation.
Sapphire.
Alumina or clay
98-5
89-50
86-0
Silica ...
0-0
5-50
3-0
Oxyde of iron -
1-0
1-25
4-0
Lime ...
0*5
0-00
0-0
t
100-0
96-25
93-0
Salamstone is a variety which consists of small transparent crystals, generally six- siprisms, of pale reddish and bluish colors. The corundum of Baitagammana is*freque n Jfound in large six-sided prisms: it is commonly of a brown color, whence it is calJe ^ ta jsthe natives cnrundu galle, cinnamon stone. The hair-brown and reddish-brown cr> s yare called adamantine spar. Sapphire and salamstone are chiefly met with in secondrepositories, as in the sand of rivers, &c., accompanied by crystals and grains of ° cI,adral iron-ore and of several species of gems. Corundum is found in imbedded cry staa rock, consisting of indianite. Adamantine spar occurs in a sort of granite. , aI1
The finest varieties of sapphire come from Pegu, where they occur in the Cap ^mountains near Syrian . Some have been found also at Hohenstein in Saxony , jsBohemia , Pay in I ranee, and in several other countries. The red variety, the ra5 V^ymost highly valued. Its color is between a bright scarlet and crimson. A perfect ^ ]above 3$ carats is more valuable than a dianjond of the same weight. If It we, ^ a ts,carat, it is worth 10' guineas; 2 carats, 40 guineas; 3 carats, 150 guineas; 6 c ® py^bove 1000 guineas. A deep colored ruby, exceeding 20 carats in weight, is ^ e Pr 0 triii,called a carbuncle; of which 108 were said to be in the throne of the Great l ,^ ]Cweighing from 100 to 200 carats each; but this statement is probably incorrect*largest oriental ruby known to be in the world was brought from China togarin, governor of Siberia . It came afterwards into the possession of Princeand constitutes now a jewel in the imperial crown of Russia. ts its
A good blue sapphire of 10 carats is valued at 50 guineas. If it weighs 20 ca^value is 200 guineas ; but under 10 carats, the price may be estimated by mulUP^ ^yerthsquare of its weight in carats into half a guinea ; thus, one of 4 carats woukl ^ ne gs4? X s O. = 8 guineas. It has been said that the blue sapphire is superior i* 1 ‘ rl ibyto the red, but this is probably a mistake arising from confounding the corun g (jjs-with the spinelle ruby. A sapphire of a barbel blue color, weighing 6 carat-?posed of in Paris by public sale for 701. sterling; and another of an indigo | iej reC ediU:>6 carats and 3 grains, brought 60/.; both of which sums much exceed what tii j Th srule assigns, from which we may perceive how far fancy may go in such n* a , * or hard-sapphire of Brazil is merely a blue tourmaline, as its specific gravity and m ^ p 0 ]i=h e “ness show. White sapphires are sometimes so pure, that when properly cut athey have been passed for diamonds. „ j en tal top aZ
The yellow and green sapphires are much prized under the names of I r s tone & l ' eand emerald. The specimens which exhibit all these colors associated mhighly valued, as they prove the mineralogical identity of these varieties. ^ colors? °.
Besides these shades of color, sapphires often emit a beautiful P^ a .-. * jjght; al1 .
chatoiernent, when held indifferent positions relative to the eye or inClL or ast el ~ ias ’some likewise present star-like radiations, whence they are called slar-ston •- ^ lC gto ae *sending forth 6 or even 12 rays, that change their place with the position toThis property, so remarkable in certain blue sapphires, is not, howevet, r 'j-j for *h egems. It seems to belong to transparent minerals which have a rnom