506 



MINERALOGY. 



Oryctogno- occur in a bed in primitive limestone in the Bannat ; 

 ^S- the grey-coloured varieties occur sometimes in veins, 

 ^Y""" ' sometimes in beds, and either in transition or second- 

 ary rocks. 



Geographic Si/Italian. It is found in the lead 

 veins of Wanlockhead and Leadhills ; also at Grass- 

 field Mine near Nenthead in Durham, and in Derby- 

 shire. 



Second Kind. 



Friable FRIABLE EARTHY LEAD-SPAR, Jameson. Zerreibliche 

 earthy Bleierde, Werner. 



External Characters. Its colours are yellowish-grey 

 and straw.yellow, which sometimes approaches to sul- 

 phur-yellow and lemon-yellow. It occurs massive, dis- 

 seminated, and in crusts. It is composed of dull dusty 

 particles, which are feebly cohering. Soils feebly. It 

 is meagre, and rough to the feel. It is heavy. 



Grognoslic Situation. It occurs on the surface, or in 

 the hollows of other minerals, and is usually accompa- 

 nied with galena or lead-glance and lead-spars. 



Geographic Situation. It is found at Wanlockhead 

 and Leadhills j Zellerfeld in the Hartz. 



Rhomboi- 2. RHOMBOIDAL LEAD-SPAR, Jameson. Rhomboedris- 

 dal cn?s giei Baryt, Mohs. 



Di-rhomboid =141 47', 81 46'. Cleavage in the 

 direction of the faces of the rhomboid, and in the direc- 

 tion of the lateral faces of the six-sided prism. Hard- 

 ness=3.5 4.0. Specific Gravity=6.9 7.2. 



This species contains two subspecies, viz. Green 

 lead-spar and Brown lead-spar. 



FIRST SUBSPECIES. 



Green lead GREEN LEAD-SPAR, Jameson. Grim Bleierz, Werner. 

 Plomb phosphate, Hatty. 



External Characters. Its colours are green, yellow, 

 and white. It seldom occurs massive, sometimes sta- 

 lactitic, reniform, and botryoidal, sometimes in distinct 

 concretions, which are granular or prismatic ; but most 

 commonly crystallized. The following are the secon- 

 dary forms : 1. Equiangular six-sided prism. 2. Six- 

 sided prism, truncated on all the lateral edges, thus 

 forming a twelve-sided prism. 3. Six-sided prism, flat- 

 ly acuminated on the extremities with six planes, whicli 

 are set on the lateral planes. The crystals are small 

 and very small, seldom middle-sized ; they are super- 

 imposed, in druses, or scalarwise, or rose-like aggrega- 

 ted. Sometimes they form velvety or moss-like drusy 

 crusts. Externally it is smooth and shining, or splen- 

 dent ; internally glistening, and the lustre is resinous. 

 The fracture is small grained uneven, passing on the 

 one hand into splintery, on the other into conchoidal. 

 The fragments are indeterminate angular, and blunt- 

 edged. It is more or less translucent, seldom nearly 

 transparent, and is sometimes only translucent on the 

 edges. It is brittle, and easily frangible. 



Chemical Characters. It dissolves in acids without 

 effervescence. 



Wanlockhead. 



Conslit. Parts. Oxide of lead 80.00 



Phosphoric acid 1 8.00 

 Muriatic acid J.G2 



Oxide of iron a trace 99.96 



Geognostic Situation. It occurs in veins and beds in 

 primitive, transition, and secondary rocks. 



Geographic Situation. It occurs along with galena 

 or lead glance, and other ores of lead, at Leadhills 

 and Wanlockhead. In England, it is met with at 

 Alston in Cumberland, Allonhead, Grasshill, and Tees- 

 dale, in Durham, and Nithisdale in Yorkshire. 



5 



SECOND SUBSPECIES. 



Oryctogno- 



BROWN LEAD-SPAR, Jameson. Braun Bleierz, Werner. "V 1 

 Plomb phosphate, Haiiy. 



External Characters. Colour clove-brown, of dif- 

 ferent degrees of intensity, rarely approaching to liver- 

 brown, sometimes so pale that it inclines to white. Oc- 

 curs massive, also in distinct concretions, which are 

 thin prismatic, and curved lamellar; and crystallized in 

 the following figures: 1. Equiangular six-sided prism, 

 which is sometimes bulging. 2. Six-sided prism, con- 

 verging towards both ends, and thus inclining to the 

 pyramidal form. 3. Acute double three-sided pyramid, 

 in which the lateral planes of the one are set on the la- 

 teral planes of the other, and in which the common basis 

 is sometimes more or less deeply truncated. The crys- 

 tals are middle sized and small, sometimes short and 

 acicular, singly imbedded, or scopiformly or globularly 

 aggregated. Surface of the crystals is sometimes black- 

 ish or yellowish brown, and rough. Internally it is 

 glistening, and the lustre resinous. Fracture small and 

 fine-grained uneven, and sometimes passes into small 

 splintery. Fragments indeterminate angular. Feebly 

 translucent, or translucent on the edges. The streak is 

 greyish-white. Rather brittle, and easily frangible. 



From Huelgoet in Brittany. 

 Constituent Parts. Oxide of lead "8.58 

 Phosphoric acid 19-73 

 Muriatic acid 1.65 99.96 



Klaproth, Beit. b. iii. s. 157. 



Geognostic Situation. It occurs in veins that traverse 

 gneiss, clay-slate, and porphyry. The veins generally 

 contain lead and silver ores, also native silver, iron and 

 copper pyrites, malachite, blende, ochry ironstone, hea- 

 vy-spar, and quartz. 



Geographic Situation. Europe. It is found at Miess 

 in Bohemia; near Schemnitz in Hungary; Saska in 

 the Bannat ; Zschoppau in Saxony ; Huelgoet and 

 Poullaouen in Lower Brittany. 

 America. Zimapan in Mexico. 



3. PRISMATIC LEAD-SPAR, or RED LEAD-SPAR, Ja- Prismatic- 

 meson. Prismatischer Blei-Baryt, Motis. Roth-Bleierz, lead spar- 

 Werner. Plomb chromatc, Hatiy. 



Prism unknown. Cleavage in the direction of a rect- 

 angular prism. Hardness = 2.5. Sp. gr. = 6.0, 6.1. 

 External. Characters. Colour hyacinth-red, more or 

 less deep or pale. Seldom occurs massive, generally in 

 flakes ; and crystallized in the following figures : 



1. Long slightly oblique four-sided prism. 2. Prism 

 acutely and obliquely bevelled on the extremities, the 

 bevelling planes set on the lateral edges. 3. Prism acu- 

 minated with four planes, which are set on the lateral 

 planes. 



Crystals generally small, thin, and always superim- 

 posed. Lateral planes formed by bevelment longitudi- 

 nally streaked, the other planes smooth, shining or 

 splendent. Internally shining or splendent, and the 

 lustre adamantine. Fracture small-grained uneven, 

 sometimes passing into imperfect and small conchoidal. 

 Fragments indeterminate angular, and rather sharp- 

 edged. More or less translucent. Gives a streak, of a 

 yellow intermediate between lemon-yellow and orange- 

 yellow. Almost sectile, and easily frangible. 



Chemical C/iaracters. Before the blowpipe it crackles 

 and melts into a grey slag. With borax it is partly 

 reduced. It does not effervesce with acid. 

 Constituent Parts. Oxide of Lead, 63.96 



Chromic Acid, 36.40100.36 



Vauquelin, Journ. des Mines, n. 34. 737- 



Geognoslic and Geographic Situations. It occurs in 



