OF CORNWALL. 199 
water it is a rich blue, but with nut or poppy oil it makes a 
deep ivory-black. Befides this black grit, there is a more folid 
kind of black copper-ore, very ponderous ; it is bliftered into large 
tubercles, by which it appears, that it is a folution of copper con- 
creted in a bed of fulphur, and covered over with a giaffy, fpark- 
ling cruft a : it may pofiibly be worth while for thofe who prepare 
paints by fire, to try whether fome valuable blue colour, fuch as 
Pruflian blue or ultra-marine , may not be extracted from the blue 
grit, Section iv, and thole two black copper earths. 
The red-ore mixed with glafly fpeckles (the cryftallized falts ofsECT.vii. 
this metal) is called the fire-ore; it rifes generally in fmall, detached Red ore. 
glebes from a bed of coarfe ochre, and the ferrugineous rubrica , co- 
vered at times with a cruft of lapideous green copper ; fome of it 
is a folution, as by the bliftered granules appears ; fome the natural 
ore ; it is very ponderous, and more valuable than any of the reft. 
Some ores of this colour break into Ihining furfaces, and refemble 
fo much the ores of filver, that fcarce any one can diftinguifti the 
laraeft grains of this fort from the argentum rubrum of Andreafberg 
in Hanover, which contains betwixt eighty and ninety parts of 
an hundred of filver, the wafte flying oft', being meer arfenick. 
This beautiful and rich ore is never faved feparately from the reft, 
although it promifes fo fair for filver. It was fuppofed by fome 
gentlemen at Leyden, to whom I fent a large fpecimen, clofe-grained 
and folid, that it contained much zink. 
The moft perfect copper, from which the before-mentioned are sect. viii. 
only fo many inferiour and different removes, is the Malleable (from Malleable 
its purity called in Cornwall the Virgin-ore) which, in fmall quan- 
tities at leaft, is found in all the moft confiderable copper-mines. It is 
varioufly combined and allayed ; fome with bafe cryftal (granulated) 
intermixed; fome with goffan, fome with white gravelly clay, fome 
in ruddle and the ruft of iron ; in fhape very various, fometimes thin 
fpread, and fhaped like leaves, now like drops and boffes, now branched, 
fringed, or twifted into wires, in hollow filagree, in blades and 
daggers, now in powder little inferiour in luftre to that of gold ; 
fometimes bliftered, at other times a congeries of combined gra- 
nules ; but which is the fineft of all, fometimes in folid lumps (as 
the Mullion copper) of feveral pounds weight, maturated, unmix- 
ed, and highly polifhed. 
Fig. 1. Virgin-ore, fomewhat bliftered ; it has feveral little co- sect.ix. 
lumns at a , croffmcr each other like bones, with knobs or bunches 
' O perSj Plate xx,i, 
* A very rare fpecimen from 
at 
