MINERALOGY. 



505 



lead-cpar. 3. Prismatic, or red lead-spar. 4. Pyramidal, 

 or yellow lead-spar. 5. Tri-prismatic, or lead vitriol *. 

 Corneous lead, Arseniate of lead, Native minium. 



I . DI-PRISMATIC LEAD-SPAR, Jameson. Di-prisma- 

 tischer Blei-Baryt, Moht. 

 f- Vertical prism =r 117 e 4'. Horizontal prism in the 



direction of the smaller diagonal = 109 Stf. Cleav- 

 ace the same. Hardness = 3.0 3.5. Sp. gr. = 6.2 

 6.6. 



This species is divided into three subspecies, viz. 

 White lead-spar, Black lead-spar, and Earthy lead-spar. 



FIRST SUBSPECIES. 



rbite lead WHITE LEAD-SHAH, Jameton. Weiss-Bleierz, Wtr. 



*. ner. Plomb carbonate, Hauy. 



External Character* Its colours are white, yellow, 

 brown, and grey. It has sometimes a tempered steel 

 tarnish. It is sometimes coloured externally yellow or 

 brown, by yellow or brown iron-ochre ; occasionally 

 gran, by earthy malachite ; and blue, by earthy blue 

 copper. It occurs massive, disseminated, in membranes, 

 MOOR) reticulated ; and crystallized in the following 

 forms: 1. Unequiangular six-sided prism, in which 

 the terminal edges are truncated. 2. Lnequiangu- 

 lar sis-sided prism, acutely acuminated with six 

 plane*, which are set on the lateral planes. S. Arute 

 double fix-sided pyramid, which is perfect. 4. Une- 

 quiangular six-sided prism, acuminated with four planes, 

 two of which are set on the lateral planes, bounded by 

 the obtuse lateral edges, but the other two are set on 

 the acuter lateral edges. 5 Acute oblique double four- 

 sided pyramid, in the lateral planes of the one are set 

 on the lateral planes of the other. It is the preceding 

 figure without the prism. 6. Long acicular and capillary 

 crystals, columnarly aggregated. 7. Occurs also in 

 twin and triple crystals. The crystals are usually 

 mall and very small ; seldom middle-sized ; are often 

 long and aciciilar, also broad and tabular. Crystals oc- 

 cur superimposed, and either single or in druses ; more 

 frequently columnarly and scopiformly, or promiscuous- 

 ly aggregated. Externally, it alternates from specular 

 splendent to glistening. Internally, it alternates from 

 shining to glistening, and the lustre is adamantine, 

 sometimes inclining to semimetallic, sometimes to resi- 

 nous. Fracture is small conchoidal, which sometimes 

 putts into uneven and splintery. Fragment* are inde- 

 terminate angular, and rather sharp-edged. Alternates 

 from translucent to transparent ; and it refracts double 

 in a high degree. Brittle, and very easily frangible. 



Conttituent Varti Oxide of lead 82 

 Carbonic acid 16 

 Water . 2100 



Klapntk, Beit. b. iii. s. 168. 



Chemical Character*. It is insoluble in water. It 

 dissolves with eServescencr in muriatic and nitric acid--. 

 Before the blowpipe it decrepitates, becomes yellow, 

 then red, and is soon reduced to a metallic globule. 



Geognottic Situatio*. It occurs in veins, and some- 

 time* also in beds, in gneiss, mica-slate, clay-slate, 

 foliated granular limestone, grcy-wacke, grey-wacke- 

 slate, and secondary limestone. 



(i'n^rajtic .Sj/ua&WIt occurs at Leadhills in 

 Lanarkshire, in vein* that traverse transition rocks, 

 in which it is associated with galena or lead-glance, 

 earthy white lead-spar, green lead-spar, lead-vitriol or 

 sulpbat of lead, sparry iron, iron-pyrites, brown he- 



matite, calamine, and blue copper ; and the vein-stones Oryctogno- 

 are quartz, lamellar heavy-spar, calcareous-spar, brown- 

 spar, and mountain-cork. It is found also with galena > p y^ >/ 

 or lead-glance at Allonhead and Teesdale in Durham ; 

 with the same ore at Alston in Cumberland, and Snail- 

 back in Shropshire. 



SECOND SUBSPECIES. 



BLACK LEAD SPAR, Jameson. Schwarz Bleierz, Black lead 

 Werner. P ar ' 



External Characters. Its colour is greyish-black, 

 of different degrees of intensity, which sometimes 

 panes into ash-grey. Occurs massive, disseminated, 

 corroded, cellular, and seldom crystallized, in small and 

 very small six-sided prisms. The surface of the crys- 

 tals is sometimes drusy, sometimes smooth, and some- 

 times longitudinally streaked. Externally it is general- 

 ly splendent, and sometimes shining. Internally it is 

 only shining, sometimes passing into glistening, and 

 the lustre is metallo-adamantine. The fracture is small- 

 grained uneven, which sometimes passes into imperfect 

 conchoidal. Alternates from translucent to opaque. 

 Its streak is whitish-grey. In other characters agrees 

 with the preceding. 



Conttitucnt Parlt. Oxide of lead 79 



Carbonic acid 1 8 



Carbon . 299 



Lampiidius, Handb. Zu. Chcni. Anal. 

 Geognottic Situation. It generally occurs in the up- 

 per part of veins, associated with white lead-spar, and 

 galena or lead-glance. 



Geographic Situation. It occur* at Leadhills; at 

 Fair Hill and Flow Edge, Durham. 



Earthy 

 lead par. 



THIRD SUBSPECIES. 

 EARTHY LEAD-SPAR, Jameton. Bleierde, Werner. 



This subspecies is divided into two kinds, viz. Indu- 

 rated earthy lead-spar, and Friable earthy lead-spar. 



Firtt Kind. 



INDURATED EARTHY LEAD-SPAR, Jameton. Verhartete Indurated 

 Bleierde, Werner. earthy lead 



External Character*. Its most frequent colours are ' 

 grey, from which it passes on the one side into yellow, 

 on the other into brown. It occurs also smoke-grey, 

 bluish-grey, and light-brownish red. It occurs mas- 

 sive. Internally it is glimmering, inclining to glisten- 

 ing ; and the lustre is resinous . The fracture is small 

 and fine grained uneven, which passes on the one side 

 into fine splintery, on the other into earthy. The 

 fragments are indeterminate angular, and blunt-edged. 

 Is usually opaque, or extremely faintly translucent on 

 the edges. It yields a brown-coloured streak. 



Chemical Characters. It is very easily reduced before 

 the blowpipe; effervesces with acids, and becomes 

 black with sulphuret of ammonia. 



Tarnowitz. 



ConttU.ParU. Oxide of lead . 6o'.00 



Carbonic acid . 18.00 



Water . . 2.25 



Silica . . 10.50 



Alumina . . 4.75 



Iron and oxide of manganese 2.22 



97/75 



John, Chem. Unt. b. ii. s. 229. 

 Geognottic Situation. The yellow-coloured varieties 



Thlitostrris 

 OL. xrr. FART n. 



, and appeari to be owing to intermixed white lead-ore or Icad-ritrioL 



3s 



