LAPIDARY.

749

sti C ' e f U5 ’ ? ni ^ ar ip e s from the combination of certain circumstances in their cutting and» uctui ' e - Lapidaries often expose the light-blue variety of sapphire to the action of

, in order to render it white and more brilliant; but with regard to those found at

fire,

t- ' . 'y- 1 vu icuuer it wnue ana more Dr:

' n ^ rance ) ® re deepens their color.n 1 . " fysoberyl, called by Hairy, Cymophane, and by others, Prismatic corundum, ranksity ■ b ar( tness to sapphire, being 8-5 on the same scale of estimation, its specific grav-foun 1 usuaU y occu rs in rounded pieces about the size of a pea, but it is also

ban ,. cr y stc ddzed in many forms, of which 8-sided prisms with 8-sided summits are per-ivh't ' 16 m °^ ^ le( liie n t. Lustre vitreous, color asparagus green, passing into greenish-the 1 t an< ^ °^ ve -green. It shows a bluish opalescence, a light undulating, as it were, intract' 6 ’ w ^ en viewed in certain directions; which property constitutes its chief at-jji 10a to the jeweller. When polished, it has been sometimes mistaken for a yellowof it° na ’ an< ^ i" rom t ts hardness and lustre is considerably valued. Good specimensot ^ e are very rare. It has been found only in the alluvial deposites of rivers, along withPaz ? S ? ec *. es °f gems. Thus it occurs in Brazil , along with diamonds and prismatic to-Prot' ,° * n Ceylon . Its constituents are alumina, 68-66; glucina, 16-00 ; silica, 6-00;a nal°- X ' 6 ^ ron ’ ox 5'de of titanium, 2-66; moisture, 0-66; according to SeyberPsPipe^ S1S - a s P e< d men f rom Brazil . It is difficultly but perfectly fusible before the blow-or ti’ Wl ^ borax and salt of phosphorus. In composition it differs entirely from sapphire,we rhombohedral corundum.

rubv Ruby, called Dodecahedral corundum, by some mineralogists, and Balas

the h 5 k^daries. Its hardness is 8. Specific gravity, 3-523. Its fundamental form isbedr exa bedron, but it occurs crystallized in many secondary forms : octahedrons, tetra-iato Ki S> an< ^ rbombohedrons. Fracture, conchoidal; lustre, vitreous ; color, red, passingspinell an< * § reen ’ yeBow, brown, and black; and sometimes it is nearly white. Red0-75 Ue consists of alumina, 74-5 ; silica, 15-5; magnesia, 8-25; oxyde of iron, 1-5; lime,fed v .• . ut l ue ll 11 discovered 6-18 per cent, of chromic acid in the red spinelle. TheSfeen ai fh^ es ex P 0Se ^ to beat become black and opaque; on cooling, they appear first"’hich ,- 1° a bnost colorless, but at last resume their red color. Pleonaste is a varietyq Dews a deep green globule with borax.

with ]*!■ s spinelie from Ceylon have been observed imbedded in limestone, mixed<li s t r i c , lca > ° r roc bs containing adularia, which seem to have belonged to a primitiveby Veo' ..^ber varieties like the pleonaste occur in the drusy cavities of rocks ejecteda long \ ’yj as - Crj-stals of it are often found in diluvial and alluvial sand and gravel,°re ) j n p 1 true sapphires, pyramidal zircon, and other gems ; as also with octahedral ironbedded • e ' aotl - Blue and pearl-gray varieties occur in Siidermannland, in Sweden , un-ion. p? § ran ular limestone. Pleonaste is met with also in the diluvial sands of Cey-ston es E wi an< ^ finel y c °l° re( l specimens of spinelle are highly prized as ornamentalhalf t]L .ben the weight of a good spinelle exceeds 4 carats, it is said to be valued at'vei°-h B ,i ? nce °f a diamond of the same weight. M. Brard has seen one at Paris which5* y ~ la grains.

the secon*)” ° r Its fundamental form is an isosceles 4-sided pyramid; and

lustre m Uar ^ b )! 'uis have all a pyramidal character. Fracture, conchoidal, uneven;"’hich w°tn ° r P er iectly adamantine; colors, red, brown, yellow, gray, green, white;Cavity 4.- ** le exception of some red tints, are not bright. Hardness, 7-5. ' Specificsa me cn n pi ^i rcon and hyacinth consist, according to Klaproth , of almost exactly theZa ' c °nia ih U6ats ’ nam ely, zirconia, 70 ; silica, 25; oxyde of iron, 5. In the whiteColor, but 1 16 1S less iron and more silica - Before the blowpipe the hyacinth loses itsfor °fnam - S not me R- The brighter zircons are often worked up into a brilliant form,c °ofound e d ntl " S watc b cases. As a gem, hyacinth has no high value. It has been oftenfecognj se( j Wl *b °tber stones, but its very great specific gravity makes it to be readily6 y

SC;, The fundamental form is a scalene 4-sided pyramid; but the secondaryJp'uninated \P ns matic character ; and are frequently observed in oblique 4-sided prisms,b^cture c p ^ anes - The lateral planes of the prism are longitudinally striated.er ully of’ Dal* 10 uneven ; lustre, vitreous; colors, while, yellow, green, blue.; gen-

'° r ding r, e shades. Hardness, 8 ; specific gravity, 3-5. Prismatic topaz consists, ac-b® a t the fac^ 2 f US ’ “htmina, 57 - 45; silica, 34-24; fluoric acid, 7-75. In a strongWfs, whictj h S r cl 7?tallization, but not those of cleavage, are covered with small blis-a- s - Its r,o"^ ver ammec b ale ly crack. With borax, it melts slowly into a' transparentdifferent fa C g s ^ er ao ' or ? Rw tincture of violets green. Those crystals which possesse big beated ° °B cl .' ? ta lhz a tion on opposite ends, acquire the opposite electricities onMost perfect crLo!?* 10 ?’ acquires positive electricity.

R ° 0rs , nlono- with bervi- topaz have been found in Siberia , of green, blue, and whitera zil, where tliev o™ m ,. t b e Uralian and Altai mountains, as also in Kamschatka ; in. t, erally occur in loose crystals, and pebble forms of' bright yel-