Metals. MINER 
fortification-agate: and, laftly, in grains loofely aggregated 
in marl ; and in form of an incruftation on coal and foffil 
wood. 
Sulphuret of iron is difpofed to undergo two very dif¬ 
ferent changes by expofure to the air; for either the ful- 
phur is diflipated; or, by abforption of oxygen, it is con¬ 
verted into fulphuric acid. In the firft inftance, the pyrites 
gradually lofes its metallic lplendour, and is ultimately 
reduced to the ftate of a brown oxyd of iron ; from its co¬ 
lour, the decompofed fulphuret is diftinguifhed by the 
epithet hepatic. This variety frequently contains gold, 
and is confequently called auriferous pyrites; but the 
gold is not chemically combined with the other confti- 
tuent parts of the pyrites ; it is Amply mixed with them ; 
and therefore, as the decompofition proceeds, its particles 
become more apparent. In the fecond inftance, the acid 
produced by oxygenation of the fulphur combines with 
the iron, and forms the metallic fait called fulphat of 
iron, or green vitriol. Radiated and ftalaftitically-formed 
mafles of pyrites are particularly fubjedtto this fpontane- 
ous alteration. 
There is no depth to which mining has been carried 
where iron pyrites is not found : one of its moft common 
appearances perhaps is under the form of cubic cryftals 
imbedded in varieties of ftate. The fubftance of foftil 
fliells, efpecially of the variety called cornu ammonis, is 
frequently pyratical. 
The variety called magnetic pyrites does not occur cryf- 
tallized : its magnetic property depends on the fmall pro¬ 
portion of fulphur contained in it. 
Iron pyrites is never worked as an ore of iron: it is 
principally valuable on account of the fulphur contained 
in it: which is either leparated by means of heat; or, in 
confequence of artificial procefl'es, is made to undergo 
that alteration which gives rife to the production of green 
vitriol. Iron pyrites may be diftinguifhed from copper 
pyrites by its greater hardnefs 5 from native gold by its 
want of malleability. 
34. Ferrum phlogifticum, or bituminous iron-ore: 
opake, of a dnfky colour, inflammable. Found in Hun¬ 
gary and Sweden, in external appearance refembling a 
piece of coal; texture friable, or rather firm, or fixed : it 
quickly kindles, and burns with a light flame, lofing 
fomething of its weight: confilts of bitumen with about 
30 per cent, of iron. 
Plate IV. fig. 1, reprefents an ore of granulated iron. 
The granulated ore is rare: it is a mals compoled of round 
grains like fmall fhot, very rich in iron, fometimes with 
Arias of various colours. The matrix is fmooth, with the 
appearance of a ferruginous brown compact ftone. Fig 2, 
iron in globules. This ore contains a number of ferruginous 
globules, imbedded in a ftony lubftance lefs compaft : the 
matrix is impregnated with an ochraceous fubftance, and 
contains much ieis iron than the globules. Fig. 3 is an 
haematites, with fmall ftriae, of a dark red colour, and the 
richeft of the kind, containing 8oibs. of iron in a cwt. 
It is uled in medicine as an aftringent. A fine fpecimen. 
Fig. 4, round red iron. This bowl of iron is grey and red- 
difh within : thefe pieces are often lo hard, that it is diffi¬ 
cult to break them with a hammer; they are not all 
equally round, but often of various forms of gibbofity. 
They are rare, and contain but little iron. Fig. 5, fparry 
iron-ore. The ore follows the natural quality of the fpar, 
being partly ftriated, partly cubical, and partly foliace- 
ous : fome of the facets are femi-tranl’parent, and lhaded 
with different colours. Fig. 6, ochraceous iron. This is 
a grey ore of iron, lhaded with black, and encrufted with 
ochre. This ore is pretty common, but not with a green 
fhade : it is rich in metal. Fig. 7, Swedith iron. Compact 
manganefe encrufted with ochre, and containing iron; 
within it is bluilh. Fig. 8 is an ore of white iron from 
Styria; it is ramified with large branches. This is a beau¬ 
tiful lpecimen, few being found fo large and fo well pre- 
lerved. It contains not much iron, and is therefore by 
modern mineralogifts feparated from the ores of iron, and 
A LO G Y. Metals, 499 
reckoned among the ftaladlitical Hones. The branches 
intertwine in the moft curious manner, and the extremi¬ 
ties glitter in the fun like the fineft barley-fugar. The 
internal fra&ure exhibits a great number of brilliant ray* 
from the centre towards the circumference. The matrix 
is a ferruginous blackilh-grey fcone. 
Stannum, Tin.—Generic characters : Silvery-white, 
tarnilhing in the air ; foftilh, very malleable and dudtile, 
not fonorous, flexible, and'crackling when bent; fpecific 
gravity, 7-291 ; eafily melting, and the furface foon be¬ 
coming covered with a grey powder, which gradually 
changes to yellow if the heat be continued ; in a very 
violent heat running into a fine white glafs ; foluble in 
acids, but not totally in the nitric ; giving the lolution 
a bitter tafte, and forming a purple precipitate when 
mixed with a lolution of gold. There are eight fpecies. 
1. Stannum nativum, or native tin. Specific charac¬ 
ter ; white, unalloyed, with metallic luftre. The exift- 
ence of native tin is queftionable. A mineral fubftance 
was met with fome years fince, in Cornwall, having lome 
of the external characters of molybdenum; it was, in 
the mafs, very brittle ; but particles were detached from 
it, which were malleable, had a metallic fplendour, and in 
every r^fpeCl refembled tin. Since that time a fubftance 
has been met with in France, which at firft was fuppofed 
to be native tin ; but, according to M. flaiiy, the fitua- 
tion in which it occurred being accurately examined, there 
appeared ftrong reafons for believing that it was an artifi¬ 
cial produCI; though no probable conjecture could be' 
formed as to the means by which it had been conveyed 
to the fpot where it was found. 
а. Stannum aureum, or yellow tin : of a gold colour, 
eafily burning with a blue flame, and leaving a white 
oxyd. Found near Gieren in Silefia, intermixed with 
other foffils, in fcarce and fmall lumps. 
3. Stannum pyriticofum, tin pyrites, or fulphuret of 
tin : yellowilh fteel-grey, with metallic luftre, of a ra¬ 
diated texture, emitting lulphurous vapours when burnt, 
and leaving a white oxyd. This has been found only at 
St. Agnes in Cornwall, where there is a vein nine feet 
wide, and twenty yards below the furface. It is foft, and 
very brittle. Specific gravity, 4-35. Contains tin 34, 
copper 36, fulphur 25, iron 3, earth 2. Klaproth. 
4. Stannum mineralifatum, or native tin-fpar : fhining, 
opake, milk-white, with a yellowifh-white ftreak. Found 
near Gieren in Silelia, and in Cornwall, of a common form, 
or in pyramids of o&ohedrons ; texture frequently fibrous 
or lamellar; when fuf’ed with borax it produces a milk- 
white glafs. Specific gravity, 6-007. 
5. Stannum fpatofum, or fpathofe tin : whitifh orbrown, 
lamellar, diaphanous, tranfparent or femi-tranfparent. 
Found in Cornwall, Bohemia, and Saxony; and is often 
confounded with tungften. It difiolves in acids, melts 
with confiderable difficulty, and is fometimes fo hard as 
to itrike fire with fteel •. its furface can be fcraped with a 
knife : it is found in mafles, and fometimes cryftallized in 
double four-fided pyramids. Colour w-hitilh, or various 
fhades of brown, with often a mixture of red. Specific 
gravity, 7. It contains from 70 to 80 per cent, of tin. 
б. Stanmim ligneum, wood-tin, or ftream-tin .- pale 
wood-colour, marked with alternate paler ftriae ; fibrous 
in a ftellate manner; flunking fire with fteel; feparating 
into layers, or breaking into wedge-form fragments. It 
is called wood-tin, from its colour; tooth-tin, from its ftiape; 
and Jiream-tin, becaufe it is found (in very fmall quanti¬ 
ties) in the ftream-works near St. Columb, and St. Denis, 
Cornwall, in fragments which are rarely equal in fize to 
a large hazel-nut. The form of thefe is often wedge- 
fiiaped, or irregularly conical; and they are indiftindtly 
marked with ftriae, radiating from the apex towards the 
bafe: the furface of the bale is frequently convex; fa 
that the fragment appears to be, if the term is admiffible, 
the leftor of a fphere. The fragments are divided into 
numerous bands of different dimenfions and lhades of co¬ 
lour, principally however of a light brown, which crofts 
thefe 
