382 Air. Brooke's Description of the [MaV, 



PonM 119° 30' 



P onT 115 



MonT 93 30 



Zoizite is crystallographically, as well as che- 

 mically, a distinct species of mineral. It has 

 been classed by the Abbe Haiiy under epidote, 

 a mistake into which he has probably fallen from observing 

 crystals of epidote apparently forming part of the mass of the 

 specimens of zoizite from Carinthia. 



Some specimens of it have been sent to this country from the 

 Tyrol under the name ofspodumene, and resembling that mineral 

 in colour, and it probably accompanies the true spodumene from 

 that locality. 



A mineral called zoizite from the Oural Mountains, which has 

 been examined chemically by Mr. Children, and found to agree 

 in its characters with zoizite, has afforded the most accurate 

 measurements of the prism. And Mr. Heuland has kindly sup- 

 plied me with other specimens of this mineral, by means of 

 which I have been enabled to ascertain that the angles of the 

 prism are the same in specimens from all the different localities 

 in which the mineral occurs. 



Its form is a rhombic prism, probably oblique from an obtuse 

 edge, the lateral planes measuring 116° 30', with a bright cleav- 

 age plane parallel to the short diagonal of the prism. 



Arseniferous Phosphate of Lead. — This substance occurs at 

 Iohangeorgenstadt in yellow hexagonal prisms, the terminal 

 edges of which are replaced by single planes. 



It presents crystalline faces after fusion by the blowpipe, as 

 phosphate of lead does, and it exhales an abundance of arsenical 

 fumes when fused on charcoal. It appears, therefore, to contain 

 both arsenic and phosphoric acids, but I cannot find any analy- 

 sis of it published. 



I have taken this notice of it for the purpose of observing that 

 the same species is found also at Beeralston in small yellow 

 hexagonal prisms, and has been called arseniate of lead ; from 

 which, however, it may be readily distinguished by its crystalline 

 character after fusion. 



Carbonate of Magnesia and Iron. — On measuring the angles 

 of different specimens of the substances which have been called 

 bitter spar, or magnesian carbonate of lime, I have found one 

 variety differing in its angle from all the others. This is the 

 yellow variety from the Tyrol, which occurs in single crystals 

 imbedded in talc or chlorite. 



Its form is an obtuse rhomboid, measuring 107° 30', the 

 corresponding angle of the true bitter spar being 106° 15'. 



On observing this difference in the angle, I dissolved a portion 

 of the yellow crystals in dilute sulphuric acid, and obtained from 



