30 MINERALOGICAL 
it. They might be eafily taken for fmall 
cubes of fluor, but their conftituent parts 
are copper and arfenic. Examined with 
the blowpipe, they fwell in little bubbles, 
and emit the fmoke of arfenic, but not 
fo much as the firft mentioned cryftals, 
nor do they run fo quickly into a grey 
metallic button. After this button had 
been melted with borax, it could be beat 
out upon the anvil into thin plates ; but 
it was harder and fomewhat more pale 
than pure copper, and had fome fpots of 
o 
a fteel colour. It would feem therefore 
that iron is mixed with it. 
Befides the tin and copper in which 
the principal richnefs of Cornwall coniifts, 
it produces alfo other remarkable foffils. 
Galena in large cubes is found at Tre- 
feavean with copper pyrites : at Pol dice 
mixed at the fame time with cuprous and 
arienical pyrites in quartz and killas: and 
at Penrofe there is a rich vein of it which 
opens upon the furface. 
Grey 
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