I R O

I RO'

( 583 )

Its colour is iron-black, often fuperficiallytarnifhed. It occurs maflive, diffeminated andcryftallized. The forms of its cryftals are,

1. The ottohedron.

2. The garnet dodecahedron.

3. A rehtangular four-fided prifm, terminatedby four-fided pyramids.

The cryftals are ufuaily either imbedded oraccumulated on each other, and are fmall andmiddle-fized. The internal luftre varies be-tween bright-filming and glimmering, and ismetallic. Its frafiture is generally coarfe or finegranular, uneven; fometimes alfo fmall con-choidal and imperfectly lamellar. It fome-times, though rarely, occurs in coarfely granu-lar and very loofe diftinot concretions. It givesa brownifh black ftreak and is confiderahly hard.The cryftals are very difficultly frangible, butthe granular varieties are more eafily broken.Sp. gr. 4.2 to 4.9.

It is not only attrafitable by the magnet, butitfelf pofleffes polarity, hence it takes up ironfilings. Before the blowpipe it becomes brownand tinges glafs of borax of a dark green colour.It has not been regularly analyzed, but is fup-pofed to be nearly a pure oxyd of iron. Whenfmelted in the large way it is faid to yield from80 to 90 per cent, of metal, but this is mani-feftly impoffible; a more probable eftimate isfrom 60 to 70 per cent. It occurs mod fre-quently in primitive mountains and chiefly ingneifs, micaceous fchiftus, chlorite flate, andprimitive limeftone: alfo in ferpentine, and inthe floetz-trap formation. When in mafs itforms beds and fometimes confiderable rock-maffes. It is ufuaily accompanied by horn-blende, granular limeftone, and garnet; alfo,though more rarely, by amianth, aftynolite,fluorfpar, coccolite, fahlite, augite, all the vari-eties of pyrites, blende, tinftone and galena.

The Mountain Taberg in Swedifh Lapland,and Pumachanche in Chili, are faid to confiftalmoft entirely of this mineral. It exifts ingreat abundance and purity in Roflagia in Swe-den , where it is manufactured into the heft bariron, fo much fought after by the Englifh manu-facturers of fteel. It alfo occurs in fufficientplenty to be fmelted in the iflands of Corfica andElba; Arendahl in Norway; in Saxony , Bo-hemia, Silefia, and the Hartz in Germany ; inmany places among the Uralian mountains inRuflia; and in Siam in the Eaft Indies.

When pure it affords the beft bar iron, butonly middling calt iron: it is eafily fufible andrequires but little flux.

2. Sub/p. Magnetic iron fand. Efenfand,Wern. Per magnetique fabloneux, Broch. 1

Its colour is deep iron black. It occurs inangular and roundifh grains from the fmalleftdimenfions to the magnitude of a hazel-nut;alfo in odtohedral cryftals. Both the grains andcryftals are externally fomewhat rough andglimmering. Internally it exhibits a bright-fhining metallic luftre. Its fra&ure is perfectlyconchoidal and rarely imperfectly foliated. Itsfragments are indeterminate and lharp-edged.It gives a greyifti-black powder. It is moderatelyhard, brittle and eafily frangible. Sp. gr. 4.6.

It is powerfully attracted by the magnet, butis fcarcely at all aCted on by the muriatic ornitric acids.

It feems to belong almoft entirely to thefloetz-trap formation, and is found imbedded inbafalt and wakke or loofe in the beds of rivers.It does not often occur in fufficient abundanceto be fmelted, yet it is employed for this pur-pofe in the Tyrol, near Naples, and in Virginia,and produces about 60 per cent, of excellentbar iron.

Sp. 5. Specular Iron Ore. Efcnglanz ,Wern.

Of this there are the turn following fubfpecies.

Subf. 1. Common Specular Iron ore. Ge-meiner Eifenglanz , Wern. Fer fpeculaire commun,Broch.

Its ufual colour is deep fteel-grey, paffingfometimes in the cryftallized varieties to ironblack, and in the maflive varieties to brownifhred. It is often tarnifhed externally, and thenprefents the blue and yellow tints of temperedfteel. It occurs in mafs, diffeminated and cryf-tallized. The forms of its cryftals are,

1. A compreffed hexahedron compofed oftwo three-fided pyramids fet bafe to bafe withthe angles of the one correfponding witli thefides of the other.

2. The fame, with the anglel'at the bafe trun-cated.

3. The cube with its edges replaced by nar-row planes.

4. A double fix-fided prifm deeply truncated.

5. A fix-fided table: fometimes feveral of.thefe are grouped together fo as to form cells.

6. A low equiangular fix-fided prifm.

7. Lenticular.

The planes of the cryftals are fometimesfmooth and fometimes ftriated, but in the cubeare always ftriated diagonally. Its externalluftre is generally bright-finning metallic. Its.frafiture is compact or foliated; the compact ia