TIN
TIN
( 415 )
5. A rectangular tetrahedral prifm termi-nated at each extremity by a tetrahedral pyra-mid, the faces of which are rhombs.
6. The foregoing, with thofe edges of theterminal pyramid that are adjacent to the prifmdeeply truncated.
7. Similar to the foregoing, only the termi-nal pyramid is much higher, and the lateraltruncatures are fo deep as to obliterate the ori-ginal rlipmboidal faces, whence refults a pyra-mid compofed of eight trapeziums.
8. The fame as the preceeding, with thepoints of the terminal pyramid truncated andreplaced by a low eight-fided pyramid, com-pofed of alternate trapeziums and long hexa-gons.
9. A cryflal originating from var. r. inwhich an oblique fection appears to have beenmade, and the two portions turned half roundon each other, fo as to form at each extremitytwo re-entering angles. Thefe half-turned orhemitrope cryftals are of particularly frequentoccurence.
The cryftals vary much in fize but are fel-dom large, and are almoft always half-imbeddedand grouped together in a confufed manner.Externa ly they are commonly fmooth, fome-times ftriated, and exhibit a bright, almoft vi-treous luftre. Internally they are fhining orgliftening, with a luftre between refinous andvitreous. The fra&ure is fmall-grained un-even, fometimes imperfectly conchoidal, andrarely lamellar. The maffive varieties prefentgranular diftinct concretions. . It varies fromfemitranfparent to op alee ; gives a grey ifh-whiteftreak-, is hard, affording fparks when {truck bythe fteel, is brittle and eafily frangible. Sp.gr. 6.7 — 6.97.
Before the blowpipe on charcoal it decrepi-tates, becomes pale and opake, and is in partreduced to the metallic ftate. It has been ana-
lyfed by Klaproth and Lampadius with the fol-lowing refults.
Klapr.
Lampad.
from Alternon.
Ehrenfriederfdorf.
77-5 —
21.5 —
16. Oxygen
0.25 —
9. Oxyd. of Iron
°-7 5 —
7. Silex
100 . .
ICO.
Tinftone occurs only in the oldeft of theprimitive rocks, as granite, gneifs, micaceousfchiftus, and fome varieties of argillaceous fchif-tus, either in veins, or beds, or diffeminated.. It
is accompanied by quartz, mica, lithomarga,talc, fteatite, fluor fpar, chlorite, topaz, apatite,wolfram, arfenical pyrites, &c. It occurs alfoin rounded fragments in alluvial bgds, formingthe fhode and ftream tin of Cornwall .
It is found in Cornwall, in Gallicia in Spain ,in the Erzgebirge on the borders of Saxony andBohemia ; in the peninfula of Malacca and theiiland of Banca in Afia, and in Chili in SouthAmerica .
It is the only ore of tin fufficiently abundantto be worked
Sp. 2. Wood Tin. Kornifches Zinnerz,Wern. Mine d’Etain grenue, Broch.
Its colour is hair-brown of different fhades,paffmg into yellowi{h-grey and Ifabella-yellow,two or more colours are oftpn arranged in pa-rallel bands in the fame fpecimen. It has hi-therto been found only in fmall rolled pieces,which fometimes are reniform, and this is pro-bably the original form of this mineral. Exter-nally it is rough and gliftening; internally ithas a glimmering fomewhat filky luftre Itsfrafture is finely fibrous, either ftraight,bundled, or diverging. Its fragments arewedge-fhaped or fpiintery. It occurs in largeand coarfe granular diftin£i concretions, whichare themfelves arranged in thin curved lamellae.It gives a (hining yellowifh-brown ftreak. Itis opake, hard, brittle, and eafily frangible. Sp.gr. 6.45.
Before the blowpipe it becomes brownifh redand decrepitates, but is not fufed or reduced tothe metallic ftate. When ftrongly heated in a.charcoal crucible, it affords according to Klap-roth about 73 per cent, of reguline tin.
This mineral has hitherto been found only inCornwall , in the parifhes of St. Columb, St.Roach, and St. Dennis, in alluvial beds accom-panied by tinftone. It is rare, and occurs onlyin fmall pieces.
Sp. 3. Bell-metal ore. Tin pyrites.Zinnkies, Wern. Etain pyriteux, Broch.
Its colour is fteel-grey, with a tinge of brafs-yellow, paffmg into yellowifh-white. It occursin mafs and diffeminated. Internally it has aweakly-fhining metallic luftre. Its fradture-is granular uneven, pnffing into fmall con-choidal, and rarely, imperfectly-lamellar. Itsfragments are indeterminate, blunt edged. Itmay eafily be fcratched by a knife, is verybrittle and eafily frangible. Sp. gr- 4.35.
Before the blowpipe it gives out a fulphur-eous odour, and fufes eafily into a blackifh flag.It tinges borax of a yellowifti green colour.
The proportion of tin which it contains is