500 Metals. MINERALOGY, Metals. 
thefe llrire at right angles. On the convex furface of 
fome lpecimens of wood-tin fmall cavities are obfervable ; 
which appear to have been formed by the impreflion of 
pyramidal.cryftals of quartz : in other inltances thefe ca¬ 
vities ar.e of a. fpherical form; and their dimenfions are 
juft’ fufficient to make them capable of containing com¬ 
mon (hot ;■ hence fpecimens of this kind are called Jhot-tin. 
Wood-tin often refembles fome of the varieties of brown 
hematitic iron-ore. ' 
The fpecific gravity of ftream-tin is very remarkable ; 
for it nearly equals that of the metal itfelf; whereas the 
fpecific gravity of other native oxyds is in general greatly 
inferior to that of the metals from whence they are de¬ 
rived. Thus, the fpecific gravity of 
Iron is 778 ; of the native oxyd 5 
Copper 
8*66 
3'9 5 
Zink 
7' 1 9 
- 3 ' 5 Z 
Bifmuth 
9*02 
4*50 
Tin . 
7*29 
very nearly 7 
The fituation in which ftream-tin is met with, and it is 
always found to occupy the loweft part of the works, is 
evidently the effect of'the great fpecific gravity of the ore; 
and all the operations of the miner connected with the 
reparation of the ore from the matrix, or from the fub- 
ftances accompanying .it, have a reference to this cliarafter. 
With this view, when the ore is difleminated through gra¬ 
nite or any other rock, thefe lubftances are broken into 
fragments of a convenient fize, and lubmitted to the 
operation of ftamping; a mechanical procefs which re¬ 
duces the mafs to a minute ftate of divifton ; and by means, 
of water, the courfe of which is directed over the pounded 
ore, the earthy particles are eafily feparated from the me¬ 
tallic oxyd ; the water walking away the former, and con¬ 
veying them to a diftance, while the latter fubfides almoft 
immediately on the fpot. 
7. Stannum amorphum, native oxyd of tin, or common 
tin-ftone : compadt, opake, of a common form, colour 
dulky, with a light grey ftreak. Found in Cornwall, 
Devonfhire, the Scilly Iftands, India, Bohemia, Saxony, 
Silefia, &c. in mafles or rounded pieces. Colour dark or 
blackifti-brown, with various ftiades of yellowilh or aftiy- 
grey or brownilh-red: it is very hard, decrepitates before 
the blowpipe, and on charcoal is partly reduced : it tinges 
borax white. Specific gravity, 6*9. Contains tin 777, 
oxygen 21*5, iron 25, filex 75. 
The tin-ore of,Cornwall is obtained either by mining 
in the common manner, or by a procefs called Jireaming. 
In the firfr inftance, the metallic vein, which is there called 
a (ode, is traced by adits or levels, which are apertures 
driven horizontally into the rock containing the lode ; or 
by Jhafts, which are fimilar apertures vertically fituated. 
In the fecond inftance, the ore is found already feparated 
from the native lode ; and, judging from its appearance 
and from local circumftanees, has been conveyed to its 
prefent fituation by rivers, or torrents of water, long ago 
dried up. The ftream-works of Cornwall are generally 
fituated in the low ground that lies between the adjoin¬ 
ing acclivities of oppolite hills; and the loweft point of 
thefe works is the angle made by the meeting of thefe ad¬ 
joining and oppofite. acclivities ; their lurface is a plane, 
fituated at different heights or diftances from this angle, 
and bounded by the fides of the hills between which it is 
extended. The meafure of this diftance differs according 
to the nature of the fpot: in fome inltances it amounts 
to many yards ; in lome, only to. a.few feet. 
The tin-ore is found always in the loweft part of the 
works ; fometimes in the form of fand, which is ufually 
of a dark-brown or black colour; fometimes in the form 
of pebbles, the fize of which, gradually increafing from 
the fmalieft particles, is occasionally equal to a large 
orange. The .(pace from the furface.of the works to the 
point where the tin-ore begins to appear, is occupied by 
common fand,.and loofe earth or clay ; depofited without 
any regularity, and often containing mofs, and branches 
of trees, and bones of men and other animals. The 
common miner, in reafoning from thefe appearances* is 
forcibly led to the conclufion, that at fome former period 
a violent rufh of water has detached maffes of tin-ore 
from the native lode ; and waffling them away, together 
with whatever oppofed its prpgrefs, has depofited thefe' 
fubftances in the fituations where they are now found ; 
and the extraordinary weight of the ore readily accounts* 
for its being conftantiy found in the loweft relative fitua¬ 
tion. 
Native oxyd of tin is met with more abundantly in 
Cornwall than any other part of the world. It occurs 
there in diftinct cryftals, and in fpecks and grains difle¬ 
minated through granite and other rocks : it is frequently 
accompanied-with earthy chlorite and tungften-. It is not 
found in many other parts of the world : the principal fo¬ 
reign mines are in Bohemia and Saxony; in Gallicia; in 
the peninfula of Malacca, and fome of the neighbouring 
iftands. It only occurs in primitive rocks ; and, as its 
veins are always divided by and never divide other veins, 
it is concluded that of all metallic fubftances its forma¬ 
tion is the moft ancient. From this ore all the tin of 
commerce is obtained. 
8. Stannum cryftallinum, or cryftallized tin : compadt, 
opake, ponderous, with a light grey ftreak, in the form 
of cryftals. Found in all tin-mines, fometimes very 
fmall and cluftered together, fometimes in larger regular 
cryftals. Colour black or brown, with generally a (hilling- 
furface; rarely red, yellowilh, orgreenifh. Found inter- 
fperfed in quartz, fluor, or other matrices, or loofe among 
the foil or land; the cryftals are very irregular, the primi¬ 
tive form of which is l'uppofed to-be a cube, but they 
commonly occur in the form of double or Angle four-fided 
pyramids with the edges beviiled. 
Plate V. fig. 1, 2. Spathofe tin.—Tin fometimes infi- 
nuates itfelf into fpar without colouring it much; and 
this fpar, being fometimes very brittle, feparates into fmall 
fragments, a number of which are fliown at fig. 1, col- 
ledted in a box ; while fig. 2 exhibits an entire mafs; the 
parts are rhomboidal; the black marks of the tin appear 
only here and there. 
Fig. 3-11. Wood-tin from Cornwall.—This wood-like 
tin-ore is a very hard fubftance, as appears from the num¬ 
ber of fmall fragments found in ftream-works, with fliarp 
angles, though fometimes, and but feldom, in a round 
pebble-like form. It feems extraordinary that many 
fmall pieces of this ore fliould be found in different ftream- 
works, but very feldom united in a mafs ; and yet they 
have the appearance of having been broken from large 
pieces, and from their fliarp angles to be natives of the 
adjoining ground ; but even with very diligent inquiry 
and fearch, large pieces are feldom to be procured. The 
following figures, from Mr. Ralhleigh’s cabinet, will tend 
to fhow moft of the varieties of this fort of ore. Fig. 3 is 
a large mafs of accumulated cryftallizations of wood-like 
tin-ore, formed in fegments of concentric circles, having 
variegated belts of different ftiades of brown, from very 
dark to very light; of a ftriatecl texture, in a folid ftone 
of rich tin-ore: it contains 63^ of tin in 100 of ore* ac¬ 
cording to Klaproth. This allay feems very exact, from 
other trials. This ftone weighs 50Z. 1 dr. and was found 
in the higher quarter of St. Auftell. Fig. 4 is a large 
piece of tin-ore, with the common wood-like tin-ore in 
the middle part of the ftone, compofed of many ftriatecl 
cryftallizations, diverging from different centres, and 
meeting at their circumferences near the middle line of 
the ftone ; the upper and lower parts of the fpecimen are 
more folid tin-ore. This ftone appears to be broken from 
a fimilar piece, if not from a lode. It is a rich tin-ore, 
and weighs 11 oz. 11 dr. and was found in Gofs Moor. 
Fig. 5 is a mafs of different globular figures of wood-like 
tin-ore, exhibiting a great variety or portions of circles, 
each (hooting from its own centre; the whole a bown co¬ 
lour, the interior part more light than the exterior, which 
is nearly black. A little quartz is mixed with this, par¬ 
ticularly on the reverie of the fpecimen here exhibited, on 
which 
