418 DESCRIPTIVE MINERALOGY. 



VAUQUELINITE. 



[In honour of the celebrated French chemist, Vau(IUELin.] 



Cupreous Chromate of Lead. Cleaveland. — Vauquelinite. Phillips, Shepard and BeudaiU. — Cupreo-Chromate 

 of Lead. TAomion. — Hcmiprismatischer Melanochlor-Malachit. Mohs. 



Fig. 500. Description. Colour dark green, approaching olive green. Streak 



siskin-green or brownish. It occurs regularly crystallized, and also 

 massive. The crystals are small. The primary form is supposed 

 to be an oblique rhombic prism. Dr. Thomson says it is a rhom- 

 boid, having nearly the same angles as chabazite. Fracture uneven. They are often com- 

 pound, as in the accompanying Fig. 500. P on P' over the summit, 134° 30' ; P on A 149° 

 {Phillips). Lustre faintly resinous, or dull. Faintly translucent or opaque. Hardness 

 from 2.5 to 3.0. Specific gravity 5.80 (Phillips); from 6.80 to 7.20 {Beudant). Alone 

 before the blowpipe upon charcoal, it melts with much frothing, and yields a few small grains 

 of lead. It is soluble in nitric acid. The solution exhibits the characters of chromic acid, 

 and causes a deposit of metallic copper upon a bar of iron, and also blades of lead upon a 

 bar of zinc. The solution of vanadiate of lead gives a copious white precipitate with nitrate 

 of silver, which is not the case with vauquelinite. 



Composition. Chromic acid 28.33, protoxide of lead 60.87, oxide of copper 10.80 

 (Berzelius). It appears to be a compound of the subchromate of lead and the chromate of 

 copper. Formula 2PbO.Cr03 + CuO.Cr03. 



Geological Situation. This mineral was first found associated with the chromate of lead 

 from Siberia, where it occurs on quartz. It has also been obtained at Pont Gibaud in the 

 Puy de Dome, and is said to accompany the chromate of lead from Brazil. 



LOCALITY. 



The only known locality of this mineral in the United States, is a mile south of Sing-Sing 

 in Westchester county, where, as we are informed by Dr. Torrey, a specimen was some 

 years since obtained. It was in the form of small mammillary concretions, and also in a gra- 

 nular and sub-pulverulent form. Colour green and brownish green. Lustre resinous. Brittle. 

 Powder greenish yellow. Before the blowpipe, it grows darker and decrepitates, but preserves 

 its green colour ; with borax, it forms a fine green bead.* 



Dr. Torrey states that the Sing-Sing mineral agrees in every respect with specimens of 

 vauquelinite from Siberia. 



* Torrey. Amials of the Lyceum of Natural History of New-York. IV". 76. 



