132 NATURAL HISTORY 
I diftinguifh, firft, into the filver or plate mundic ; fecondly, the 
brafs or pyrites aureus of Grew ; and, thirdly, the brown colour : 
the other colours are no more than a thin film or fediment, which 
water, either from its own impregnation, or the nature of the fofiil 
it refts upon, depofites upon the furface. 
The texture of mundic is either fibrous and radiated as in pyrite 
nodules, or flaky and tabulated, or wavy and of crooked fibres. 
It is found fometimes folid in large glebes and plates, fometimes in 
grains and detached mafles from two inches diameter and under, 
or, laftly, in micaceous granules, either loofe as fand, or fixed in 
incruftations. 
sect viii. There are very few copper lodes, if any, but what have this 
Its combi- femimetal (which may be called a kind of wild, mock-copper) 
coppe n r. With attending as it were upon them; and therefore, in fearching for 
copper, it is reckoned a great encouragement to meet with mundka 
The mundic does not intimately incorporate itfelf with the ore of 
.copper ; for copper, in its mineral ftate being ufually of clofe con- 
fiftence, repels the mundic, which is therefore eafily feparated from 
it either by breaking off that which is fixed with hammers, or 
by walking away the fmall in water, or by evaporation in the 
furnace. 
sect. ix. But mundic unites more clofely with our tin-ores, efpecially 
with tin. when found in a lax fandy ftate, oftentimes as moift and foft as 
mud : in this cafe the mundic mixes intimately with the tin ; and, 
being fpecifically heavier than the tin-ore, will not feparate from 
the lame by wafhing as other impurities will, but impoverifhes the 
tin, and makes the produd fo brittle, that the tin is worth little or 
nothing. To deftroy this connexion therefore, we have recourfe to 
the following method : When the tin-ore has been ftamped, that is 
bruifed fufficiently and pulverized by the mill, we put it into a 
furnace ereded purpolely for roafting it, called a Burning-houfe. 
Here the fire mull be managed and kept very moderate, and the 
tin-ore raked and ftirred well every quarter of an hour, otherwife 
the tin will fufe (efpecially in the hotteft part of the furnace), and 
then it muft undergo another expenfive trituration in the ftamping- 
mill. The gentle fire evaporates the arfenical and fulphurous parts 
of the mundic fooner or later, according to the quantity it has to 
work upon. 500 pounds weight of black-tin, ftrongly impreg- 
nated with mundic, will take twelve hours roafting to evaporate the 
mundic, .but the moderately infeded ore will throw oft the mundic 
in eight hours; fo that nothing but the earthy and lighter parts 
remaining 
