FEL

F EL

( 428 )

It melts at a high heat into a porous porcelainTuafs. It appears to be nearly connected with:tranfition griinftein, and probably forms the ballsof fome of thofe porphyries which are commonlyranked as hornftone porphyries: indeed certainvarieties of this and fplintery hornftone refembleeach other fo clofely in their external charactersthat it is by no means eafy to afcertain t-o whichfpecies they belong. Hornftone however is ingeneral both harder and tougher, and is infufibleper ft before the blowpipe, whereas continuousfelfpar is fufible, though it often requires for thispurpofe a very high and long continued heat.

V. Labradore Felspar. Labradoijtcin,Wern. Feldfpath tpalin , Hauy.

The proper colour of this mineral is fmoak-jp'ey or dark alh colour, but on account of thefmall crevices between the lamella: of which itis compofed, it prefents a moft beautiful play■of vivid tints varying according to the politionin which it is viewed: of blue it exhibits all.the varieties from violet to fmalt-blue; of greenit difplays the pure emerald green and variousother tinges approaching to blue on one handand yellow on the other; of yellow the ufuallhades are gold and lemon yellow verging intodeep orange and thence into rich copper-redand tombac brown. The parts exhibiting thefebeautiful colours are difpofed in irregular fpotsand patches, and the fame fpot if held in dif-ferent pofitions difplays various tints. It hashitherto been found only in detached rolledfragments. Internally it is lhining palling intofplintery, with a luftre between pearly and vi-treous. Its principal fraCture is perfectly lamel-lar in two directions, the lamellae crofting eachother at right angles; its crofs fradture is fome-what conchoidal : it breaks into rhomboidalfragments with four fpecular faces. It ufuallyexhibits large granular and fometimes thoughrarely ftrait lamellar, diftinct concretions. Itis ftrongly tranflucent palling into femi-tranf-parent. Sp.gr. 2.6 to 2.7.

_ It is fufible without addition before the blow-pipe into a white enamel.

The only analyfis that has yet been made ofthis mineral Is by Bindheim, according to whom

.it contains

SilexAlumine - >Sulphated lime -Oxyd of copperDitto of iron

Lofs -

69.5

13.612.

0.7

°-3

xoo.o

It was fir ft difeovered by the Moravian mif-fionaries on the Illand of St. Paul on the coaftof Labrador, and has finee been found in In-germannland in Norway , and in the vicinity ofLake Baikal in Siberia . It is fometimes accom-panied by mica, black fchorl and iron pyrites.

It is in confiderable eflimation on account ofits beautiful colours for ornamental purpofes.

On comparing the refults of the analyfis offelfpar by Vauquelin and Chenevix, both ofthem chemifts of acknowledged ability and feru-pulous accuracy, it is impoflible not to be ftruckwith furprize at the remarkable difference whichappears between them. That potalli fhouldappear in one analyfis and not in the other is noextraordinary circumftance, becaufe without aparticular examination for this very objeCt thepotalh would remain undetected and its amountwould be transferred to the general account oflofs : the lofs therefore in Mr. Chenevix’s analyfisought to be equal both to the lofs and potafli inVauquelin’s; but the amount fet down as lofsin both cafes is nearly equal, therefore the dif-ference between the earthy and metallic pro-ducts of the two analyfes amounts to 13 percent, being the proportion of potafli as afeer-tained by Vauquelin. In order to obtain fomeclue by which to account for this difference, themethods of analyfis purfued by thefe chemiftshave been compared and examined, but withoutobtaining much fatisfaction.

Mr. Chenevixafter finely pulverizing thefelfpar, treated it with cauftic potalh in a filvercrucible, and the whole was then brought to alimpid folution by muriatic acid. 1. The liquorwas evaporated to drynefs and the faline refiduedigefted in a flight excefs of muriatic acid, awhite powder remained infoluble which wasfilex. 2. The muriatic liquor with the wafh-ings of the filex was then mixed with ammonia,and a copious precipitate was thus obtained. 3.This precipitate was then difiolved in muriaticacid, and afterwards boiled with an excefs ofpotafli by which the iron was depofited •, andthe addition of muriat of ammonia then threwdown the alumine. 4. The ammoniacal liquorNo. 2, was treated with carbonat of potafli, bywhich carbonat of lime was procured. Thismethod of analyfis appears quite unexceptionableas far as the earthy and metallic contents areconcerned, and, if carefully performed, thereappears no reafon why its refults fliould not beconfidered as giving the true proportions andquantities of the earths and oxyd of iron con-tained in felfpar, proper allowance being firit

k Phil. Tranfi for 1802 p. 333.