FEL

FEL

( 427 )

Is not fo hard as quartz, yet will fcratch glafs :it is brittle and eafily frangible. Sp. gr. 2.27to 2.70.

It melts before the blowpipe without additioninto a white fomewhat tranflucent glafs.

Felfpar has been often analyfed and with verydifferent refults. The three laft analyfes of thisfubftance and perhaps the moft to be dependedon, are, one of common felfpar and another offelfpar from the fand of Ceylon, by Chenevix,and one of the green Siberian felfpar by Vau-quelin.

Com. F. Ceylon F. SibcrianF.

Silex - - 64. — 68.5 — 62.83

Alumine - 24. — 20.5 — 17.02

Lime - - 6.25 — 7. — 3.

Oxyd of iron 2. — 1.5 — 1.

Eotalh - - o — o — 13.

96.23 97-5 9 6 -85

Felfpar when expofed to the weather acquiresgradually an earthy appearance, and at lengthpaffes into porcelain clay. It alfo occurs in aftate of femi-decompofition in feveral varietiesof granite and porphyry, where it cannot havebeen affected by the atmofphere. When inthis ftate it is ufually of a yellowilh or reddiffi-white colour, a faintly glimmering luftre, anda fracture imperfectly foliated palling intoearthy: it breaks into indeterminately angularfragments, is opake and confiderably fofter thancommon felfpar. A very light coloured varietywas analyfed by Vauquelin, and found to con-tain Silex - - - 74

Alumine - - 14.5

Lime - - - 5.5

94.0

Lofs - - 6

100.

Some of the coloured tranflucent varietiesof felfpar contain particles of mica difperfedthrough their fubftance, and thefe when theftone is expofed to the light form fo manyluminous points, which relieve the colour ofthe felfpar and give the whole a fpangled ap-pearance that has a pleafing effect: in fomeinftances however thefe brilliant particles feemto be occafioned merely by fiffures in variousdirections. When felfpar exhibits this appear-ance it is called Aventurine (a term alfo appliedto a fimilarly glittering variety of Quartz).The green Siberian felfpar fometimes contains

fpangles of a remarkably brilliant filvery mica,forming a very elegant aventurine. Anotherfine variety has been procured from Cedlovatoi,an illand in the White Sea, not far from Arch-angel , confifting of a femitranfparent hyacinth-brown bafe with gold coloured fpangles. Theaventurine of Spain is the moft familiar toEuropean lapidaries, but this is a variety ofquartz.

Common felfpar is the moft generally dif-fufed, both as to its local and geological fixa-tion, of any other mineral except perhaps quartz.It is an effential conftituent of granite andgneifs, and frequently occurs in micaceous andargillaceous fchiftus : it forms a large proportionof all filenite, and is contained abundantly inalmoft all porphyries : it is occafionally thoughrarely found in primitive limeftone : it aboundsin primitive, tranfition and fecondary griinftein,and frequently though in fmaller proportion inmoft of the other rocks belonging to the trap-formation : it alfo abounds in the greater partof the real lavas.

III. Compact Felspar. Dicker Felfpath .Emmerl. Felfite, Kirw.

Its colour is bluifh white paffing into fky-blue, or greenifh-white paffmg into brownifh-green. The blue variety occurs in mafs, thegreen is either diffeminated or cryftallized. Itsluftre is gliftening. Its fradture is very imper-fectly lamellar approaching to fplintery: itsfragments are indeterminately angular: it isfeebly tranflucent, and though hard confiderablyinferior in this refpedt to quartz.

Before the blowpipe it is difficultly fufible-without addition, into a frit or imperfedt glafs.It has not been analyfed.

The blue compadt felfpar was difeovered byWidenmann at Krieglach in Stiria , forming agranitic mafs with white quartz and filvery white-fomewhat undtuous plates, which have beenconfidered by fome mineralogifts as mica, byothers as talc. The green varieties occur in.green porphyry and grunftein.

IV. Continuous Felspar, Kirw.

Its colour is reddiffi-grey or flefh-coloured, orpale reddilh yellow, or olive green. It occursin mafs and generally contains hornblende orcommon cryftallized felfpar difperfed through,it in various proportions. It is fometimes dullbut generally poffeffes a feeble glimmering luf-tre : it is tranflucent at the edges: its fradtureis fine-fplintery paffing into uneven earthy j itsfragments are indeterminately angular. Itshardnefs is fully equal to that of common fel-fpar and it is lefs brittle.

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