550 



MINERALOGY. 



flryctogno- 



CHKTSO- 

 LITE. 



Prismatic 

 chrysolite. 



Chrysolite. 



Olivine. 



TOUHMA- 



LINE. 



It horn- 

 boidal 

 Tour- 

 maline. 



ly crystallized in very oblique four-sided prisms. Mas- 

 sive varieties occur in curved lamellar distinct conci'*- 

 tions. Externally, lustre splendent ; internally, alter- 

 nates from glistening to shining, and is vitreous, slight- 

 ly inclining to resinous. Fracture fine-grained, un- 

 even, or conchoidal. Alternates from perfectly tran- 

 sparent to feebly translucent. 



Chemical Characters. Easily fusible with ebullition 

 into a bottle-green glass, which by continuance of the 

 heat becomes nearly black. 



Constituent Parts. Silica, 50.50 



Alumina, 16. 



Lime, 17. 



Oxide of Iron, 950 



of Manganese, 5.25 



Potash, 0.2593.50 



Klaproth, t. v. p. 28. 



Geognoslic Situation. Occurs in primitive moun- 

 tains, in rocks of gneiss, mica-slate, clay-slate, and 

 hornblende-rock, and is found in Cornwall, and in 

 various districts on the continent of Europe. 



GENUS IX. CHRYSOLITE. 

 Prismatic. Vitreous lustre. Hardness = 6.5 7.0. 

 Sp.gr. = 3.3 3.5. 



1. PRISMATIC CHRYSOLITE, Jameson. Prismatis- 

 cher Krisolith, Mohs. Peridot, Haijy. 



Prism = 131 48'. Cleavage perfect, in the direc- 

 tion of the shorter diagonal, and less so in direction of 

 the longer diagonal. 



Two subspecies, viz. Chrysolite, and Olivine. 



FIRST SUBSPECIES. 



CHRYSOLITE, Jameson. Krisolith, Werner. 

 External Characters. Colour green. Occurs in 

 angular pieces, roundish pieces, and often crystallized 

 in a four and six-sided prisms, variously acuminated, 

 and bevelled, and truncated on the lateral edges. In- 

 ternally, lustre splendent and vitreous. Fracture con- 

 choidal. Transparent, and refracts double. 

 Constituent Parts. Silica, 39.00 



Magnesia, 43.50 



Iron, 19.00 101.50 



Klaproth, Beit. b. i. s. 110. 



Geognoslic and Geographic Situations Is found in al- 

 luvial soil in Upper Egypt, and on shores of the Red Sea. 

 Uses. It is cut and polished, and made into neck- 

 laces, hair ornaments, and ring- stones. 

 SECOND SUBSPECIES. 

 OLIVINE, Jameson. Olivin, Werner. 

 External Characters. Colours olive-green, and yel- 

 low. Occurs massive, in grains, and in roundish 

 pieces. When crystallized, which is rarely the case, 

 it is in the form of rectangular four-sided prisms, 

 which are always imbedded. Massive varieties occur 

 in small and angulo-granular concretions. Internal- 

 ly, lustre shining and glistening, and vitreo-resi- 

 noiis. Fracture small-grained uneven, sometimes pass- 

 ing into imperfect small conchoidal. Translucent, pass- 

 ing into semi-transparent, seldom transparent. 



Geognoslic and Geographic Situations. It occurs im- 

 bedded in basalt, greenstone, porphyry, and lava, ge- 

 nerally accompanied with augite, in Scotland, Germa- 

 ny, Italy, and other countries. 



GENUS X. TOURMALINE. 



One axis. Rhomboidal. Hardness = 7.0. 7.5. Sp. 

 gr. = S.0,_3.2. 



This genus contains one species, viz. Rhomboidal 

 Tourmaline. 



1. RHOMBOIDAL TOURMALINE. Rhomboedrischer 

 Tunnalin, Mohs. 



Rhomboidal. Rhomboid 1 33 2t? Cleavage rhom. Oryctogno. 

 Boidal, and in direction of sides of a six-sided prism. y- 



It is divided into two subspecies, viz. Tourmaline V -"V ' 

 and Schorl. 



FIRST SUBSPECIES. 



TOURMALINE, Jameson. Turmalin, Werner. Tourma- 



Internal Characters Its principal colours are green, line, 

 brown, red, blue, yellow, and white. Occurs very 

 seldom massive, or in prismatic concretions ; scarcely 

 ever disseminated ; oftener in rolled pieces ; but most 

 frequently crystallized, in three, four, six, and nine- 

 sided prisms, variously acuminated. The lateral planes 

 are generally cylindrical convex, and deeply longitudi- 

 nally streaked ; the acuminating plrties are mostly 

 smooth and shining : sometimes the planes on one ex- 

 tremity are smooth, but on the other rough. Internal- 

 ly lustre splendent and vitreous. Fracture nearly 

 perfect, and small conchoidal. Alternates from near- 

 ly opaque to completely transparent. Refracts double 

 in a middling degree. When viewed perpendicular to 

 the axis of the crystal, it is more or less transparent, 

 but in the direction of the axis, even when the length 

 of the prism is less than the thickness, it is opaque. 



Physical Characters. By friction, it exhibits signs 

 of vitreous electricity ; by heating, vitreous electricity 

 at one extremity, and resinous electricity at the other. 

 Chemical Characters. Before the blowpipe it melts 

 into a greyish-white vesicular enamel ; but the red-co- 

 loured Siberian tourmaline is infusible. 



Green Tourmaline from Brazil. 

 Constituent Parts. Silica, 40. 



Alumina, 39. 



Lime, 3.84 



Oxide of Iron, 12.5 

 Oxide of Manganese, 2. 

 Loss, 2.C6 100 



Vauquelin, Ann. de Chim. N. 88. p. 105. 

 Geognoslic and Geographic Situations Tourmaline 

 occurs in primitive rocks in Scotland, England, Ger- 

 many, Norway, Italy, and many other countries. 



Uses. The green, blue, and brown varieties are 

 sometimes cut and polished,, and worn as ornamental 

 stones. 



SECOND SUBSPECIES. 



COMMON SCHORL, Jameson. Gemeiner Schorl, Wer. Common 

 External Ckantcters. Colour velvet-black, of various Schorl, 

 degrees of intensity. Occurs massive, disseminated, 

 and frequently crystallized, in three, six, and nine-sided 

 prisms, that present various acuminations, truncations, 

 and bevelments. Occurs in granular and prismatic 

 concretions. Internally its lustre is intermediate, be- 

 tween shining and glistening, and is vitreous. Frac- 

 ture intermediate between conchoidal and uneven. 

 Opaque. Affords a grey streak. 



Common Schorl from Eibenstock. 

 Comtituent Parts Silica, 36.75 



Alumina, 34.50 



Magnesia, 0.2.5 



Oxide of Iron, 21.0 

 Potash, 6.098.50 



Klaprolh's Beitrage, b. 5. s. 148, 149- 

 Physical Characters. Exhibits the same electrical 

 properties as tourmaline. 



Geogiioslic and Geographic Situations. Occurs in 

 primitive mountains in most extensive alpine districts 

 in Europe ; and also in Asia, Africa, and America. 



GENUS XI. GARNET. GAUNET. 



Tessular, pyramidal, prismatic. If red, the sp. 

 gr. = 3.7. and more. It'black, sp. gr. = 3.9. and less. 



