520 



MINERALOGY. 



Oryctogno- Geognostic Situation. It occurs principally in the 

 Xj s *'_,_. amygdaloidal cavities of amygdaloid, and incrusting 

 the agates found in that rock. It also occasionally co- 

 lours sandstone, and is disseminated in porphyry. 



Geographic Situation It is a frequent mineral in 

 the amygdaloid of Scotland ; it occurs also in that of 

 England and Ireland. 



Uses It is used as a pigment in water-painting, and 

 is the mountain-green of painters. 



SIXTH SUBSPECIES. 

 Talc. TALC, Jameson. Talk, Werner. 



This species is divided into two kinds, viz. Common 

 Talc and Indurated talc. 



Common 

 Talc. 



First Kind. 

 COMMON TALC, Jameson. Gemeiner Talk, Werner. 



External Characters Common colours white and 

 blue. Occurs massive, disseminated, in plates, reni- 

 form, and botryoidal ; in distinct concretions, which 

 are large, coarse and small granular ; also narrow or 

 broad and stellular or promiscuous radiated, which are 

 again collected into other concretions, having a wedge- 

 shaped prismatic form. Sometimes crystallized in small 

 six-sided tables, which are in druses. Generally 

 splendent; shining; pearly; semi-metallic. Frag- 

 ments wedge-shaped, seldom splintery. Translucent ; 

 in thin folia transparent. Flexible ; not elastic. Sec- 

 tile. Feels very greasy. 



Chemical Characters. It becomes white before the 

 blow-pipe, and at length, with difficulty affords a small 

 globule of enamel. . 



Constituent Parts, Silica, . 61.75 



Magnesia, 30.50 



Potash, . 2.75 



Oxide of Iron, 2.50 



Water, . 0.25 



Loss, . 2.25 



Klaproth, Karst. Tab. s. 43. 



Geognoslic Situation: It occurs in beds in mica- 

 slate and clay-slate, and in a similar situation in granu- 

 lar limestone and dolomite; also in cotemporaneous 

 veins, in beds of indurated talc, serpentine, and por- 

 phyry ; and in the renifonn external shape in tinstone 

 veins. 



Geographic Situation It is found in Aberdeenshire, 

 Banffshire, and Perthshire. 



Uses. It enters into the composition of the cosmetic 

 named rouge. 



Second Kind. 



Indurated INDURATED TALC, or TALC SLATE, Jameson. Ver- 



Talc. harteter Talk, Werner. 



External Characters Colours grey and green. Oc- 

 curs massive, and rarely in fibrous distinct concretions. 

 Lustre shining, passing to glistening; pearly. Frac- 

 ture curved slaty, passing into imperfect foliated. 

 Fragments tabular. Strongly translucent on the edges ; 

 sometimes feebly translucent. Rather sectile. Rather 

 easily frangible. Not flexible. Feels greasy. 



Geognostic Situation It occurs in primitive moun- 

 tains, where it forms beds in elay-slate and serpentine, 

 and is associated with amianthus, chlorite, rhomb-spar, 

 garnet, actynolite, quartz, kyanite and grenatite. 



Geographic Situation It occurs in Perthshire, Banfl- 

 shire, and the Shetland islands. 



Uses It is employed for drawing lines by carpen- 

 ters, tailors, hat-makers, and glaziers. The lines are 



not so easily effaced as those made by chalk, and be- ryctogno. 

 sides remain unaltered under water. '7- 



SEVENTH SUBSPECIES. 



NACRITE, Jameson Nacrite, Bronsniart. Erdieer Nacrite. 

 Talk, Werner. 



External Characters. Colours greenish-white, and 

 greenish-grey. Consists of scaly parts, which are Wore 

 or less compacted ; the most compact varieties have a 

 thick or curved slaty fracture. Strongly glimmering ; 

 pearly ; inclining to resinous. Friable. Feels very 

 greasy ; soils. 



Chemical Characters. It melts easily before the 

 blowpipe. 



Constituent Parts. Alumina 

 Magnesia, 

 Lime, 

 Potash, 

 Water, 



81.75 

 0.75 

 4.00 

 0.50 



13.50 100.50. 

 John. 



Geognostic and Geographic Situations This is a 



very rare mineral ; it occurs in veins with sparry iron- 

 stone, galena, iron-pyrites and quartz, in the mining 

 district of Freyberg in Saxony ; Gieren in Silesia ; and 

 Sylva in Piedmont. 



EIGHT SUBSPECIES. 



POTSTONE, or LAPIS OLLARIS, Jameson. Topf- Potstone. 

 stein, Werner. 



External Characters. 'Colour greenish-grey, of dif- 

 ferent degrees of intensity ; darker varieties incline to 

 leek-green, and blackish-green. Occurs massive, and 

 in granular concretions, which are indistinct. Inter- 

 nally glistening, inclining to shining ; pearly, inclin- 

 ing to resinous. Fracture curved, and imperfect foliat- 

 ed, which passes into slaty. Fragments indeterminate 

 angular, or slaty. Translucent on the edges. Affords 

 a white-coloured streak. Perfectly sectile. Feels 

 greasy. Rather difficultly frangible. 



Chemical Character. It is infusible before the blow- 

 pipe. 



Geognostic Situation. It occurs in thick beds, in pri- 

 mitive clay-slate. 



Geographic Situation. It occurs abundantly on 

 the shores of the lake Como in Lombardy, and at 

 Chiavenna in the Valteline; also in different parts 

 in Norway, Sweden, and Finland. 



Uses. When newly extracted from the quarry it is 

 very soft and tenacious, so that it is frequently fashion- 

 ed into various kinds of culinary vessels, which harden 

 in drying, and are very refractory in the fire. 



NINTH SUBSPECIES. 



STEATITE, or SOAPSTONE, Jameson. Speckstein, Steatite. 

 Werner. 



External Characters. Colours white, reddish- white, 

 and yellow. Sometimes marked with spotted and 

 dendritic greyish-black delineations. Occurs massive, 

 disseminated, in crusts, reniform ; and also in the fol- 

 lowing figures : 



1. Equiangular six-sided prism, acutely acuminated 

 on both extremities with six planes. 2. Acute double 

 six-sided pyramid. 3. Rhomboid. 



The six-sided prism, and six-sided pyramid, are from 

 rock-crystal, and the rhomboid from calcareous spar. 

 Both appear to be supposititious, and are small or middle 

 sized, generally imbedded in massive steatite. Lateral 

 planes transversely streaked, and the acuminating planes 



