MINERALOGY. 



rather eafily frangible, and melts before the blow-pipe into 

 a white enamel. When pounded it gelatiniz^'S in acids. The 

 fpecitic gravity is 2.58 to 2.61. According to Klaproth, 

 the conftituent parts are, 



Silex .... 46.50 



Alumine ... 30.25 



Lime ... 0.75 



Potaih ... 18.00 



Oxydofiron . - i.oo 



Water . . - 2.00 



According to Vauquelin, 

 Silex 

 Alumine 

 Lime 



Potafh and foda 

 Oxyd of iron 



9S.50 



44.00 



3 4. GO 

 0.12 



16.50 

 4.00 



98. 62 



This mineral has liitherto been found only in the rock 

 named zircon fienite. ( See Zircon 5;Vn;Vf.) It is clafled 

 by Mr. Jamefon in the felfpar family ; but is placed by 

 Werner between jafper and cat'sneye. 



Elastic Mineral Pitch, or Elaflic Bitumen. Mineral 

 caoutchouc. Bitume elajiiqiie, Hai'iy. See Bitumen. 



Electrum, an argentiferous goldore, or native alloy. 

 Its colour is a palebrafs-yellow. It is not foluble either in 

 nitrous or uitro-muriatic acid. It contains, according to 

 Klaproth, 



Gold - - . 64 



Silver . . . ^6 



It occurs at Schlangenberg, in Siberia. 



Emerald, Emeraude verte, Haiiy. See Emerald. 

 Falfe emeralds are fometimes offered for fale, which are 

 either green fluor fpar, green quartz, or prafe. The eme- 

 rald of Bralil is fometimes the green tourmaline. The true 

 emerald is harder than quartz. The beryl and the emerald have 

 both the fame primitive form of the cryftal or the hexahe- 

 dral prifm. The terminal planes of the emerald are rough, 

 thofe of the beryl fmooth. The emerald agrees in chemical 

 compol'ition with the beryl, both containing from thirteen to 

 fourteen parts of the newly -difcovercd earth glucine ; but 

 the colouring matter of the emerald chrome is wanting in 

 the beryl. See Gem. 



Emery, Corindon granulaire, Haiiy. (See Emery.) 

 This mineral owes its hardneis to an intermixture of 

 blue corundum. See Adamantine Spar, and Corun- 

 DUM, Addenda. 



Epidote. (See Pistazite, and Thallite. Under 

 the latter article, for Arundel in Norway r. Arendal.) 

 Epidote occurs at the Malvern-hills in Worcefterrtiire, at 

 Wallow Cragg near Kefwick in Cumberland, and near 

 Marazzion in Cornwall. 



Epsom Salt, Native, or fulphate of magnefia, occurs as 

 an efflorefcence at Hurlet near Paifley, and fometimes is 

 found efflorefcent on old walls, and on the furface of different 

 rocks, particularly gypfum, fand-ilone, clay, and compaiS; 

 Hme.ftone. 



EucLABE. See Euclare. 



Fahlerz, Werner ; grey copper ore. See Copper- 

 Ores. 

 Vol. XXXIX. 



Felspar. (See Felspar.) The name of this mineral 

 appears to be derived from the Saxon term fell, a mountain, 

 iUll ufed in the northern counties of England ; hence felfpar, 

 in its original figniiication, denoted mountain fpar. In the 

 mineralogical fyilems of Werner and Mr. Jamefon, the fel- 

 fpar family comprifes various fpecies of minerals, which are 

 fuppofed to be nearly alHed to felfpar. The felfpar fpecies 

 is alfo divided into adularia, glaffy felfpar, Labrador felfpar, 

 common felfpar, difintegrated felfpar, and compaB felfpar. 



Adularia. (See Felspar.) — The forms of cry ftals of adu- 

 laria arethefame asthofeof commonfelfpar. It polfeffes double 

 refraftion. It melts before the blow-pipe into a tranfparent 

 white glafs. Adularia occurs in veins in granite and gneifs, 

 ill various parts of Aberdeendiire and Bamfshire, in the ifle 

 ofArran, and in the granite of Switzerland, France, and 

 Gerip.any. The largeft and moft beautiful cryilals are found 

 in the mountain of Stelia, a part of St. Gothard. Rolled 

 pieces liaving a beautiful pearly light are collefted in the 

 ifland of Ceylon. The variety which exhibits a llrong pearly 

 light is cut in a femi-globular form, and is fold under the 

 name of morn-flone, and is ufually worn as a ring-ftone. 



Glajfy Felfpar occurs always cryftallizcd in broad reftan- 

 gular four-fided prifms, bevelled on the extremities. Thefe 

 cryilals are very much cracked, and always imbedded. It is 

 tranfparent, and has a fplendent \'itreous luftre internally. 

 Its other characters agree with adularia. It occurs in pitch- 

 ilone and trap in various parts of Scotland. 



Labrador Felfpar. See Felspar. 



Common Felfpar occurs varioufly cryftallized. Haiiy enu- 

 merates more than twenty of its fecondary fonns ; feveral of 

 them are reprefentcd Plate I. Jigs. 8, 9, 10, 1 1, 12, &c. Cryf- 

 tallography. The primitive form is an oblique-angled paral- 

 lelopiped. The ftrufture is perfectly lamellar, with a double, 

 very diftinft, reftangular cleavage, and an oblique indiilinft 

 cleavage interfefting the two former. The four rectangular 

 planes have fplendent faces ; the faces of the oblique cleav. 

 age are dull. This remarkable charafter is peculiar to felfpar, 

 and may very frequently beobfervedin the rhomboidal frag, 

 nients of this mineral. Felfpar has been frequently analyfed 

 with different refults. According to Berzelius, the moil pro- 

 bable compoiition of common felfpar, fo far as we can calculate 

 it from the many analyfes of which we are in poffeffion, is, 

 that the alumine bears the fame proportion to the potafh as 

 in alum, and that the filica contains three times the oxygen of 

 the bafe. The following is therefore a comparifon between 

 the calculated and experimental refults, according to the 

 principles of Berzelius's new fyflem of mineralogy. See 

 Systems of Mineralogy. 



Silica 

 Alumine 

 Potafli 

 Lime 

 Protoxyd |^ 



of iron j " 



The lime and protoxyd of iron are regarded as accidental 

 admixtures. Felfpar is one of the principal conftituent in- 

 gredients of many of the rocks called primary, in many of the 

 trap rocks, and many of the lighter.coIoured lavas. It forms 

 aneffential conllituent part of granite, gneifs, fienite, green, 

 flone, and forms the bafe of many porphyries, and the rock 

 c:A\eAtuhite-Jlone. (See White-Stone.) In green-flone, the 

 felfpar is often tinged of a green colour, from the admixture 

 of hornblende oraugit. In many of the porphyries, it exills in 

 a compad Hate, or as compaa felfpar. The colours of compact 

 felfpar are various Ihades of white, grey, green, or red ^'- - 

 4 B 



The 

 lamellar 



