DIAMOND. 
The furface of the natural cryftals, efpecially the cane 
al, is fomewhat dull and chatoyant. is appearance whic 
generally reprefented as the effe@ of a thin cruft, appears . 
be caufed merely by the faliant edges of the lami h 
the cryftal confifts. When its ae arereduced to perfect 
{moothnefs bs grinding and polifhing. the diamond is of ex- 
treme brilliancy, far furpaffing every other fubflance in luftre, 
and the lively play of prifmatic colours, which dart from it 
in lines of light, whenever its pofiti ion, with regard to the 
e leaft variation. e fraéture 
t on 
the (absroidal varieties, 
plates; thefe are of intents hardnefs, and cannot be either 
fplit, or very highly ‘aewnae they are — ay by 
the glaziers and engravers on gem e gro into 
a powder, and ny loyal in the polithing of oes dia- 
3. 
The hardnefs of oe = is ee to that of all other 
ete ; it yields however to corundu long-continued 
fri€tion. It is brittle ave frangible without much difficulty. 
Les fp. gr. varies from 3.518 to 3.5 
Diamond, even when rough, dine by friGtion t 
vitreous or pofitive electricity. 
when expofed either to the entire rays of the fun, or to 
blue ones alone, when cd galeens a the prifm, oe oncen- 
trated on the diamond gee of alens. A fimilar ef- 
fe 
[o) 
fa) 
< 
=. 
re) 
a 
— 
oO 
nN 
B+ oy 
—s 
oa 
ao 
re) 
[) 
ry 
is 
= 
3 
bate 
5 
x 
Diamond, when heate to the cempersture of an 
copper, and ha fed to acurrent of air, is gradually, but 
completely co a it is eae ae by a luminous areo 
Ja during the proc olly converted into carbonic 
acid, and the oe eottilt of pure carbon, as we have al- 
re eady mentioned under that article. 
The art of cutting and polifhing diamonds was probably 
known to the ai . indooftan and China at a véry 
only material ne in the Eat for th 
was produced on 
quence of this hint, conftru&ed a polifhing wheel, on which, 
by means of diamond powder, he was enabled to cut and po- 
ih this fubftance, in the fame way as other gems are wrought 
ry. Previoufly to this difcovery, diamonds;were fet 
in jewellery, Laearthe in the —— in which ares arrived ihe 
e the oes i rons were mu 
ftate the oe particulars on the siete of Jellies? Pr’ 
treatife of Diamonds. 
‘Vou. XI. 
P 
diamo 
It becomes phofphorefcent | 
the 
Diamonds are cut and aga hee by jewellers into 
brilliants han rofe diamonds ; the former being for the moft 
part made out of the seeds cryftals, and the latter from 
the {pheroidal varieties. To fafhion a rough diamond into a 
brilliant, the firft ttep is to modify the faces of the original 
oto sai : that t 
two pyram all n exact {quare, and the axis of the 
ery eal twice ne length of one of the fides of the 
fquare. The oftohedron being thus re&ified, a fection is 
to be ‘made, parallel to the common bafe, or girdle, fo as to 
cut off 5 gine of ca whole height from the upper pyramid, 
and eth fr m the lower one.. The fuperior and larger plane, 
thus ‘produced is TT - table, and the inferior and {maller 
one is nam et: in this fate it is called a oa i 
Jquar de diamo o convert it into a brilliant, two 
triangular fac pe are placed on each fide of the table, thus 
changing it from a {q lozenge-fhaped fa- 
cet is alfo placed at cach of the four corners of the table, 
and another lozenge extending lengthways along the whole 
of a ae of the original {quare of the table, which, with 
ity ma 
he regular rofe diamond is formed by r salecbing a regu- 
ar ocagon in the centre of the table-fide of the ftone, and 
Berend it by eight right-angled triangles, the bafes of 
which correfpond with the fides of the cétagon; beyond 
thefe is a chain of eight trapeziums, and another of fixteen 
triangles. The collet-tide a confilts of a minute central 
otagon, from every angle o 
edge | of the eile. forming de 
ch of whic 
eccle proportions, fo much is cut away, that the a of 
the polifhed gem is _ more than half that of the rough 
es ee whence the value of 
a’ med oan o that of a fimilar rough 
diamond of twice pas weight, exclufi ve of the coft of the 
Goins thip. The“ we eight, an rei ently the value, 
of diamonds, is eftimated in carats ; one of which is equal 
to four grains, and difference between the price 
of one diamond and another, ceteris paribus, is as the {quares 
of their refpective weights. hus the value of three dia- 
monds of one, two, a three carats’ weight refpedctively, 
is as one, four, and n ec pee price of rough 
diamonds, that are wo a wo s-about 2/. fter- 
ling for th 
the value of a es diamond, afcertain its weight in 
carats, and fractions of a carat, muitiply this by two, then 
‘multiply this laft produé into itfelf, and finally multiply this 
latter {um by 24, Hence a wrought diamond of 
x Carat, is worth £8 
2 - “ - ge 
3 - - r 72 
4. * - - 128 
5 = = += 200 
@ . = = 288 : 
4C 4 Carate 
