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XIX. ^ Description of Matlovkite, a new Oxy chloride of Lead, 

 By R. P. Greg, Jun., Esq.^ 



MR. WRIGHT of Liverpool has recently obtained from the 

 old heaps of the level mine at Cromford, near Matlock, 

 a small number of specimens of the murio-carbonate of lead, or 

 phosgenite of Haidinger ; and he has also found a few specimens 

 of another ore of lead, differing in appearance from any of the 

 known salts of that metal. 



At my request this mineral has been examined by Dr. Robert 

 Angus Smith of Manchester, and his analysis of it has afforded 

 the following results : — 



Chloride of lead .... 55-17^^' 



Oxide of lead 44-30() 



Moisture -072 



99-549 

 The proportions by theory would be — 



Chloride of lead 55-46 



Oxide of lead 44*53 



99-99 



This gives a definite chemical composition of 1 atom of chlo- 

 ride of lead combined with 1 atom of oxide of lead ; differing in 

 this respect from Mendipite, in which the proportion of chloride 

 to that of oxide is as 1 to 2. 



The specific gravity of Matlockite is 7*21, and its hardness 

 2*5 to 3. Colour yellowish, with sometimes a slight greenish 

 tinge ; its lustre is adamantine, and occasionally pearly, and it 

 'is transparent and translucent. It cleaves, but not readily, 

 "^parallel to P. Its fracture is uneven and slightly conchoidal. 

 It decrepitates in the flame of the blowpipe, but with care is 

 reduced to a grayish-yellow globule. 



It occurs in tabular ciystals, generally thin and superimposed 

 on each other, and occasionally slightly cuiTcd ; but my friend 

 Mr. "W. G. Lettsom has a perfect transparent crystal an inch 

 square and an eighth of an inch thick. 



The primitive form is a light square prism ; and the following 

 figui-e, drawn by Professor Miller of Cambridge, who has also 

 corrected the mcasurcd angles, represents all the modifications 

 hitherto observed : — 



♦ Communicated by the Author. 



