526 



MINERALOGY. 



KVAXITX. 



Prismatic 

 Kjanite. 



SroDc- 

 JIENE. 



--. , Jsnestous-trerno- 



lite ; at Modum cobalt mines, also in Norway, along 

 witt common hornblende, cobalt-glance, and copper- 

 pyrites. 



GENUS II. KYANITE *. 

 Disthene Spath, Mohs. 



Three axes. Cleavage prismatic. In the most per- 

 fect cleavages, the hardness is = 5 ; on the angles it is 

 = 7. Sp. gr. = 3.5 3.7. 



This genus contains one species, viz. Prismatic Kya- 

 nite. 



1. PRISMATIC KYANITE, Jameson. Prismatischer 

 Disthene Spath, Mohs. Kyanite, Werner. 



Prism = 102 50'. Cleavage prismatoidal. 



External Characters." Colours blue, bluish-grey, white, 

 sky-blue, celandine-green, and greenish-grey. The va- 

 rieties are often marked with blue-coloured flame deli- 

 neations. Occurs massive and disseminated ; also in dis- 

 tinct concretions, which are large and longish angulo- 

 granular, and also wedge-shaped prismatic, which are 

 straight or curved, and sometimes disposed in scopi- 

 form or stellular directions. It is sometimes regularly 

 crystallized. 



1. Oblique four-sided prism, truncated on the two 

 opposite acute lateral edges. 2. Preceding figure, in 

 which all the lateral edges are truncated. 3. Twin- 

 crystal: it may be considered as two flat four-sided 

 prisms joined together by their broader lateral planes. 



The narrow lateral planes are longitudinally streaked, 

 and glistening: the broad are smooth, or delicately 

 transversely streaked and splendent. Crystals middle- 

 sized, small, and very small ; are singly imbedded, or 

 intersect one another. Lustre splendent and pearly. 

 Fragments splintery, or imperfectly rhomboidal. Mas- 

 sive varieties translucent. Crystals in general trans- 

 parent. Rather brittle. Easily frangible. 



Chemical Character. It is infusible before the blow- 



pipe. 



Conslit. Paris. 



Silica, . 



Alumina, 



Iron, 



Trace of Potash. 



43.00 

 55.50 

 0.50 



99.00 



Klaproth, Beit. 



b. v. s. 10. 



Geognostic Situation. It has been hitherto found only 

 in primitive mountains, where it occurs in compact 

 granite, mica-slate, and talc-slate, accompanied with 

 several other minerals. 



Geographic Situation. It occurs in primitive rocks 

 near Banchory in Aberdeenshire, and Boharm, in Banff- 

 shire ; in mica-slate near Sandlodge, in Mainland, the 

 largest of the Shetland Islands. 



Uses. In India it is cut and polished, and sold as an 

 inferior kind of sapphire. 



GENUS III. SPODUMENE t. 



Three axes. Cleavage prismatic. Three cleavages 

 parallel with the axes, nearly of equal perfection. Hard- 

 ness = 6. Sp. gr. = 3.O. 3.1. 



PREH- 



NITE, 



f !"* v y J. * M ' ' y , 



Prism nearly = 100. Cleavage three-fold two of Sp(xlu - 

 the cleavages parallel with the lateral plaiW, and a mene * 

 third with the shorter diagonal of the basis of the prism. 

 External Characters Colour intermediate between 

 greenish-white and mountain-grey, and sometimes 

 passes into oil-green. Occurs massive, disseminated, 

 and in large and coarse granular concretions. Cleavage 

 shining. Fracture glistening. Lustre pearly. Frac- 

 ture fine-grained uneven. Translucent. Uncommonly 

 easily frangible. 



Chemical Characters. Before the blowpipe, it first 

 separates into small golden-yellow coloured folia ; and 

 if the heat is continued, they melt into a greenish-white 

 coloured glass. 



Conslit. Parts. Silica, . 6t.4 



Alumina, . 24.4 



Lime, . 3.0 



Potash, . 5.0 



Oxide of Iron, . 2.2 99.0 



Vouquelin, Hauy's 



Tabl. p. 168. 



Geognostic and Geographic Situations This mineral, 

 which occurs in prismatic rocks, was first discovered 

 in Suclermanland, in Sweden, and afterwards in Ire- 

 land, and in other countries. 



GENUS IV. PREHNITE. 

 Prehn Spath, Mohs. 



Three axes. Cleavage axifrangible. Hardness 

 = 6.07.0. Specific gr. = 2.83.0. Not blue. 



This genus contains one species, viz. Prismatic Preh- 

 nite. 



1 PRISMATIC PHEHNITE, Jameson. Prismatischer 

 Prehn Spath, Muhs. Prehnite, Werner. 



Prism = 108. Cleavage axifrangible. 



This species is divided into two subspecies, viz. Fo 

 liated Prehnite, and Fibrous Prehnite. 



FIRST SUBSPECIES. 



FOLIATED PHEHNITE, Jameson. Bliitriger Prehnite, Foliated 

 Werner. Prehnite. 



External Characters. Colours green, white, and 

 grey. Occurs massive, and in distinct concretions, 

 which are large, coarse, and fine angulo-granular, and 

 also thick and wedge-shaped prismatic. Sometimes 

 crystallized. The following are some of the secondary 

 forms which the species assumes : 



1. Oblique four-sided table sometimes truncated ei- 

 ther on all its terminal edges, or only on the acute ed- 

 ges. When the truncations on the edges increase 

 very much, there is formed, 2. An irregular eight-sided 

 table. W T hen the truncations on all the acute edges 

 increase considerably, there is formed, 3. An irregular 

 six-sided table. When these truncating planes increase 

 in magnitude, and when the table at the same time be- 

 comes thicker, and the obtuse edges are slightly trun- 

 cated, there is formed, 4. A broad rectangular four- 

 sided prism, rather flatly bevelled on the extremities, 



Prismatic 

 Prelmite. 



* Kyanilf., from the Greek word xvxnt, Mky-blve, a frequent colour of this mineral. 



( On exposure to the blowpipe, it first separates into golden-coloured scales, and then into a kind of powder or ash ; hence the name 

 Sfodumene, from eroivti, 1 change into ash, or rnfas> ashes. 



J According to some analyses, 'it contains Sper cent, of a new alkali named Rthiia. 



