„6 NATURAL HISTORY 
N°. vii. What we callCornilh diamonds are figured cryftals, and among 
cryftals we fliall treat of them ; but fome of our cryftals are tinged 
with green : they are of the Emerald kind ; what I have feen came 
moftly from a copper-work in the parifh of Camborn, called the 
Long-clofe : the Oriental emerald is a moil beautiful gem; for 
the occidental, the jewellers x ufually fell this tinged cryftal, com- 
mon cryftal being as hard as the occidental emerald ; with us it is 
angular or columnar, but beffc when found in the pebble form, of 
which I have yet met none in Cornwall. 
N°. viii. Some of our cryftals are alfo of a fea-green or beryll 
colour, and the fame which authors call the Pfeudoberyllus : after 
burnt red-hot, they will retain their fhining in the dark for a few 
minutes only, in this falling fhort of the fmaragdus which fhines a 
confiderable time y , but, like that, change their green into a pale fky- 
blue whilft hot, but recover their native colour as they cool. 
N°. ix. But of our curious green ftones, none come near the colour and 
polifh of a green cupreous incruftation found in Huel-fortune, in the 
parifti of Ludgvan. Its texture is ftratous, cruft within cruft ; its 
furface puculated ; the tubercles which it forms on the ftones, are 
fometimes an inch in diameter, fometimes fmall, and either per- 
fectly round or truly oval ; the colour fo deep a green, and fo high 
a polifh, that I have obliged feveral gentlemen with fome to fet in 
rings, for which nature has fitted them without the aid of a jew- 
eller. This comes very near to the properties of the occidental 
turcois, and has been taken for fuch by Naturalifts. I have, from 
the fame place, this copper of a blueifh green clouded, but the 
green appears even there in fome parts, and in the greateft part of 
the fpecimens, the green is predominant and unmixed. The blue- 
turcois is generally efteemed a precious ftone, but indeed no other 
than foflil bone, or ivory faturated with copper diffolved in an al- 
kaline menjiruum ; the green-turcois is the fame fubftance inti- 
mately penetrated by a cupreous matter diflolved in an acid men- 
jiruum ^ but this precious ftone from our Cornifti mines is the aerugo 
or a plain folution of copper, as appears by its forming itfelf into 
threads and ftratous incruftations z . I have met with none of this 
kind of any value but from this work, and it has been found there 
only in one fmall cavity of about one foot and a half in diameter a . 
1 Hill, 596. Grew’s Muf. R. S. page 284. 
y Dr. Grew’s Muf. R. S. page 287. a Fig. xiv. and xv. Plate XXI. have their tu- 
z “ The turcois is much fofter than cryftal.” bercles of this beautiful green enamel. 
C H A P. 
