508 



MINERALOGY. 



OryctognO' 

 sy. 



Filament- 

 ous arse- 

 niate of 

 lead. 



reddish-brown and brownish-red ; externally ochre- 

 yellow, and straw-yellow. Occurs reniform and tu- 

 berose ; also in curved lamellar concretions. Internal- 

 ly shining and resinous. Fracture conchoidal, some- 

 times inclining to even and uneven. Opaque. Soft 

 and brittle. Specific gravity 3.933, Karstcn, 



Chemical Characters. It is insoluble in water. Be- 

 fore the blowpipe on charcoal is gives out arsenical va- 

 pours, and is more or less perfectly reduced. It colours 

 glass of borax lemon-yellow. 



Constituent Parts. Oxide of Lead 35.00 

 Arsenic acid 25.00 



Water . 10.00 



Oxide of iron 14.00 

 Silver . 1.15 



Silica . 7.00 



Alumina . 2.00 95.15 

 Biiidlieim, in Beob. u. Endeck. de Berl. Ges. Natf. 



. Fr. iv. s. 374. 



Geographic Situation. It has been hitherto found 

 only in one mine, near Nertschinsky in Siberia. 



SECOND SUBSPECIES. 



FILAMENTOUS AHSENIATE OF LEAD, Jameson. Flock- 

 enerz, Karsten. 



External Characters Colours green and yellow. 

 Occurs massive, in granular concretions, and either in 

 small acicular six-sided prisms, which are collected into 

 flakes, or in very delicate capillary silky fibres, which 

 are transparent, slightly flexible, and easily frangible. 

 Specific gravity 5.0, 6.4- 



Constituent Parts. Oxide of Lead 69-76 

 Arsenic Acid, 26.4 



Muriatic Acid 1.58 Gregor. 



Geographic Situation. It occurs in the mine of Huel. 

 Unity" in Gwennap in Cornwall ; at St. Prix, in the 

 Department of the Soane and Loire in France. 



Earthy ar. 



-.ornate i) f 

 lead. 



THIRD SUBSPECIES. 



-Erdige 



Order III. 



KLRATE. 



EARTHY ARSENIATE OF LEAD, Jameson, 

 Bleibliithe, Havsmann. 



External Characters Colour yellow. Occurs in 



crusts. Fracture earthy. Friable. 



Geosnostic and Geographic Situations. It occurs along 

 with filamentous arseniate of lead at St. Prix ; and also 

 n ear St. Oisans. 



* NATIVE MINIUM, or NATIVB RED OXIDE OF LEAD. 



Jameson Naturliche Menninge, Roth Bleioxyd, Haus- 



mann. 



External Characters Colour scarlet-red. Occurs 

 massive, amorphous, and pulverulent ; but when exa- 

 mined by the lens, exhibits a crystalline structure, like 

 that of galena, on which it generally rests. 



Chemical Characters Before the blowpipe, on char- 

 coal, it is first converted into litharge, and then into 

 metallic lead. 



Geognostic and Geographic Situations. It is found 

 in Grassington Moor, Craven ; Grasshill Chapel, Wier- 

 dale, Yorkshire. On the Continent it is found in the 

 mine of Hausbaden, near Badenweiler, on galena, and 

 associated with quartz. 



ORDER III. KERATEf. 



No metallic lustre. Streak colourless. Sectile. Clea- 



COIHIOOI 

 SUTBR. 



vage is neither distinctly axifrangible nor prismatoidal. Ofyctogno- 

 Hardness ranges from 1 to 2. specific gravity from 4 to s y- 

 o* 



GENUS I. CORNEOUS SILVER. 



Three axes. Cleavage invisible. Hardness = 1.0, 

 2.0. Spec. grav. =: 4.6. 



This genus contains one species, viz. Hexahedral 

 Corneous Silver. * Earthy Corneous Silver. 



1. HEXAIIEDRAL CORNEOUS SILVER, Jameson. H*xahe- 

 Hexedrisches Perl Kerat, Mohs. Hornerz, Werner. dral c r- 

 Argent muriate, Hauy. neousiiJ. 



Tessular. Cleavage not visible. Malleable. 



External Characters. Most frequent colour pearl- 

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

 the other white, and further, into leek-green. On ex- 

 posure to light, it becomes brownish. Occurs massive 

 in prismatic and granular concretions, in thick flakes, 

 disseminated, in egg-shaped pieces, hollow in the cen- 

 tre, and the hollows lined with crystals. The crystals 

 are the following : 



1. Cube. 2. Octahedron. 3. Rhoraboidal dodecahe- 

 dron. 



Crystals small and very small, occasionally aggrega- 

 ted in rows, or in a scalar-like form. External surface 

 smooth, sometimes marked with little hollows. Exter- 

 nally shining, but becomes gradually duller on expo- 

 sure: internally intermediate between shining and glist- 

 ening, and the lustre resinous. Fracture conchoidal, 

 sometimes inclines to earthy. Fragments indeterminate 

 angular and blunt-edged. Translucent, or only feebly 

 translucent on the edges. Retains its colour, and be- 

 comes more shining in the streak. Is malleable. Flexi- 

 ble, but not elastic. 



Chemical Characters. It is fusible in the flame of a 

 candle. 



Constituent Parts. Silver, 67-75 f 



Muriatic Acid, 14.75 

 Oxygen, . 6.75 



Oxide of Iron, 6.00 



Alumina, . 1 .75 

 Sulphuric Acid, 0.2597-25 

 Klaprolh, Beit. b. iv. s. 13. 



Geognoslic Situation. It occurs in silver veins, and 

 generally in their upper part. These veins traverse 

 gneiss, mica-slate, clay-slate, grey-wacke, porphyry, 

 and limestone, and contain, besides the corneous silver, 

 various ores. 



Geographic Situation. Europe. At Huel-Mexico 

 in Cornwall. 



Asia. In Siberia, it occurs along with native gold. 



America. This mineral, which is so seldom found 

 in Europe, is very abundant in the mines of Catorce, 

 Fresnillo, and the Cerro San Pedro, near the town of 

 San Luis Potosi. 



EARTHY CORNEOUS SILVER-ORE (J), Jameson. Er- Eartl 

 diges Hornerz, Karslen. corneous 



External Characters. Internally the colour is pale silver-ore. 

 mountain-green, inclining to greyish- white ; externally 

 it has a bluish-grey tarnish. Occurs in thick crusts. 

 Internally dull. Fracture coarse and fine earthy. Frag- 

 ments blunt angular. Very soft, almost friable. Streak 

 shining and resinous. Sectile. Heavy. 



* Kcrate, from the Greek word *<{, fiorn, given to it on account of the species resembling horn in general aspect and tenacity. 

 This mineral appears to be a mechanical mixture of corneous silver and clay, and hence it is placed beside it, but not as a variety of 

 the species. 



