5:ARTHS. siliceous. 44- Feldfpatum. 
44" FELDSPATUM. Conflfting of the greater 
part filica, ibme alumina and potafs, and a very 
fmal! quantity of lime and oxyde of iron : hard, 
lightilh, fhining, lamellar, breaking into frag- 
ments which prefent 4 faces, rfiouldering into 
argil, parafitical: not effervefcing with“nitric 
acid, eafily melting without ebullition into a 
pellucid glafs. 
^icum, Reddifh-brown, of a glaffy luftre, and fomewhat fplinr 
tery fradure, breaking into cubic fragments which 
are not fpccular, falling fpontaneoufly into cruftoft 
fragments. 
Petrilite, Cubic fclfpar. Kir^wan niintr. \,p. 325. 
Found, though rarely, in Saxony, of a common form, diapha- 
nous or fomewhat opalce ; fragments cubic or inclining to 
that form, the faces of which are not polifhed : is very brit- 
tle, and at 160® of heat whitens and concretes without an/ 
farther fign of fofion: fpeciiic gravity 3,081. 
Ofitlgare, Of a glaffy Juftrc and foliated texture, breaking into 
rbomboidal fragments with 4 fpccular faces. 
Spatum fixum fcintillans. Syst, not. xii. 3. p, i r, 6. 
Spatum fcintillans. Croujl. miner, 66. H. 
Spatum durum. Wall. min. (>i. 
Common Felfpar. Kirnuan mineral, i. p, 317. 
Cointiion Fclfpar. SchmeiJJer mineral, l.^. 132, 
Common Felfpar. '■rhomjonchetn,, 3. p. 554. 
y. Opake. 
.Spatum campeftre. SyU. nat. xii, 3. p, 50, «. 12. 
Spatum fcintillans. Wall. J'yst, miner. \, p. 205. «. i, 
2. Tranfparent. 
Spatitm filicum. Sfjl.nat. xii. 3. 7). 50. n. 13. 
Spatum fcintillans. WalLjyst. min, i. p.zab. n. z. 
3. Of a common form, 
4. In the form of cryllals, 
Spat, fcintill. cryitaliis. Wall. fyst. i. p. 207. n. 3. 
Spat, fcintill. drulicum, Cromt, mineral. 66. 2, 
a. The cryftals prifmatic. 
The pril'ms acicular, 
b. The cryftals parallelepidid, ' 
c. The cryftals thicker, with the fidps more equal, 
In 4-fided right angles. a 
In 6-fided right angles. 
