zinc. 281 



it is moderately brittle and easily frangible. The specific gravity 

 is from 3*7 to 4. It is infusible before the blow pipe. The 

 massive brown blende of Allonheads in Northumberland, consists 

 according to Dr. Thomson, of zinc 58*8, sulphur 23 - 5, iron 8*4, 

 silica 7'0. Blende may be distinguished from galena by its streak 

 and powder, which are yellowish grey, and from other ores which 

 resemble it by the sulphureous odour it emits when thrown into 

 an acid, or triturated in a mortar. Blende is found in all the lead- 

 mines in England and Scotland, and also in* those on the conti- 

 nent. The common name given to this mineral by the English 

 miners is Hack jack. 



Sp. 2. Carbonate of Zinc, or Calamine. — This ore, as Mr. 

 Bakewell justly observes, has not the appearance of a metallic 

 mineral. The colours are various shades of white, grey, greenish 

 or yellowish -grey and also brown. It is divided by some mine- 

 ralogists into three sub-species ; viz. sparry calamine, compact 

 calamine, and earthy calamine. Sparry Calamine occurs crysta- 

 lized in acute or obtuse rhomboids and in four-sided tables, either 

 perfect or variously modified. The external lustre of the crystals 

 is between vitreous and resinous ; the structure is imperfectly 

 laminar ; it is more or less transparent, and yields easily to the 

 knife. The specific gravity is about 4 "30. It is infusible, but 

 looses about 34 per cent, by ignition ; it dissolves with efferves- 

 cence in muriatic acid. Its constituents are oxide of zinc 65'2, 

 carbonic acid 34*8 — 100. Smithson. Compact Calamine is opaque 

 and has less lustre than the crystalized ; its colours are grey, 

 yellow, and yellowish-brown. It occurs in stalactitical, reniform, 

 or botryoidal masses, also cellular, and in pseudo-morphous crys- 

 tals, (PI. XXXVIII. fig. 2,) and incru sting other minerals. It is 

 opaque or slightly translucent on the edges, dull, very feebly glim- 

 mering and resinous. The fracture is granular, splintery, even or 

 flatly conchoidal. Earthy Calamine is greyish, yellowish-white, or 

 yellowish brown, and is earthy, dull, and soft, yielding to the nail. 

 That of Bleiberg, in Carinthia, consists, according to Smithson, of 

 oxide of zinc 3T4, carbonic acid 13*5, water 15 , 1 = 100 , 0. 



Calamine, after it has been calcined and reduced to a fine 

 powder by levigation, {Calamina prceparata, Ph. L.) is used medi- 



