The Chemistry, Properties and Tests of Precious Stones

ard

series, for no matter how colour, lustre, general beauty and even rarity may entitle a stone to t

s of hardness. The most popular and reliable table is that of Mohs, in which he takes talc as the softest of the rarer minerals and classes this as No. 1; from that he goes by gradual steps to the diamond, the h

lc

k s

er

cit

hite

3-

ors

tit

pta

(vario

nite

tite

lazuli

(various)

te 5-1/

dian

ne 5

rious) 5

rite

soli

spa

lar

on s

psi

pyr

ador

quo

mene

hich embraces the Agat

toid

ote

rase

o "Red Garnets"

ite

ite

ystal,Amethyst, Jasper, C

de

water sapph

erite

ee also Garnet

aline

usite

ase

olite

on 7

uamarine, o

kite

in

pa

obery

embracing the Rub

mon

arranged in their respecti

es, each with a sharp edge, is kept for the purpose of scratching and being scratc

Ta

salt, o

alc

luo

pat

els

Qu

To

oru

Dia

of increasingly higher degrees, till no scratch is evident under a magnifying glass. Thus if quartz ceases to scratch it, but a topaz will do so, the degree of hardness must lie between 7 and 8. Then we re

o. 6 stones; one made of tool steel, up to 7; one of manganese steel, to 7-1/2; one made of high-speed tool steel, to 8 and 8-1/2, and so on, according to temper; so that from the scratch whic

ace of a real ruby, which is hardness 9, or a No. 9 needle, would reveal too deep or powdery a scratch; also its possibility of being scratched by a topaz or a No. 8 needle, would alone prove it false, for the corundum group, being harder than No. 8, could not be scratched by it. So would the expert go down the scale, the tiny scratches becoming fainter as he descended, because he would be a

inctions of picking out the hardest of certain stones of the same kind, in which cases only the expert judge can decide with exactness. Accurate in this the expert always is, for he judges by the

other unerring tests of extreme severity, any one of which would prove it false, if it chanced to be so, though some stones are m

5-1/2 to 6-1/2 inclusive. All stones differ slightly, though almost all may be said to fit their position in the scale; but i

it. On a soft stone being cut by a hard one, little or no sound is heard, but there will form a plentiful supply of powder, which, on being brushed off, reveals a more or less deep incision. But as the stones approach one another in hardness, there will be little powder and a considerable increase in the noise; for the harder are the stones, cutting and being cut, the louder will be the sound and the less the powder. An example of this difference is evident in the cutting of ordinary glass with a "set" or "glazier's" diamond, and with a nail. If the diamond is held properly, there will be heard a curious sound like a keen, drawn-out "kiss," the diamond being considerably h