78 Discovery of the Vauquelinite. 



his analysis of the red lead ore of Siberia,* (the ore in which 

 chromium was discovered by that celebrated chemist) ; but he 

 does not appear to have regarded it as a distinct species. 

 Cleaveland places it as a sub-sjjecies, after the chromate of lead. 

 It was first, I believe, raised to the rank of a species by 

 Leonard, and adopted by Berzelius, who notices it in his essay 

 on the blowpipe, under the name of Vauquelinite. Most of the 

 modern writers on mineralogy, consider it as distinct, both in 

 chemical and ptrysical characters from the red ore of chrome.f 

 In the system of Mohs, Vauquelinite is still placed in the ap- 

 pendix which contains Xheproposed species, or such as are not 

 yet fully established. It must occupy this place in any system 

 based on physical characters alone, until its crystalline form 

 can be clearly determined ; and unfortunately it has hitherto 

 only been found, either massive, or in crystals so microscopic, 

 that they cannot be submitted to the goniometer.^ 



The Vauquelinite is one of the rarest minerals known. Not- 

 withstanding it is nearly forty years since it was discovered, 

 there is but one undoubted locality of it recorded : this is the 



* This mineral is not a dioliromate as stated by Turner, (ed. 5. p. 570,) but 

 a compound identical with tho ordinary artificial chrome yellow. It is only red 

 in a crystalline state, and becomes yellow when reduced to powder, liko the red 

 chromate of potassa, and some other red crystalline matters. When it was more 

 abundant it was used as a yellow, not as a red pigment. There is, however, 

 frequently occurring with the red lead ore, a distinct species, lately determined 

 by Hermann, and called by him Melauochroito. It is crystallized, and its pow- 

 der is of a red colour. Dr. Thomson (Outlines of Mineralogy, dec. 1. p. 661) 

 regards it as a Subsesquichromate of Lead. 



f Dr. Thomson (1. c. p. 516) says that the Vauquelinite is a compound of two 

 atoms of chromate of lead, and one atom of oxido of copper; but Berzelius 

 (Traiti, 4. p. 365) calls it chromate plwinbico-cuivrique sesquibasique, and his 

 yiew of its composition is probably correct. Tho results obtained by the analy- 

 sis of Berzelius were 



Chromic acid - - - - 28.33. 

 Protoxide of Lead - - 60.87. 

 Oxide of Copper - - • 10.80. 



J Perhaps even these minute crystals are merely phosphate of lead. See 

 Phillip's Mineralogy, p. 350. 



