600 



magnesia, but no lime. The three specimens, therefore, 

 differ as to the nature and relative proportion of their con- 

 stituents. I may add, that it is not possible to represent 

 the composition of any two of them by the same formula; so 

 that, admitting the correctness of the published analyses, 

 we are entitled to conclude that minerals really different are, 

 in works upon mineralogy, confounded together under the 

 name of Jade or Neptrite. 



Of the ores of mangeneus, the first I shall notice is a spe- 

 cimen of psilomelanane, the black haematite of the older mi- 

 neralogists, which I received some months since from R. W, 

 Townsend, Esq., and which occurs a little to the north of 

 the village of Glandore, in a mixed schistoze and arenaceous 

 rock, which is coloured by Mr. Griffith, as old red sand- 

 stone. S. G. = 4.071. Hardness between fluor spar and apa- 

 lite, occurs massive, but more generally in botryoidal and 

 concretionary forms. The following are its constituents, 

 determined by an analysis very carefully conducted : 



(1) (2) 



Silex 8.592 



Barytes 5.362 0.069 



Oxide Copper 1.254 0.031 



Red Oxide Mang.(Mn304) 74,574 > _Deutox. 31.241 0.393 



Oxygen 7.212 5 "Perox. 50.545 1.152 



Water 3.006 0.334 



Confining our attention to the oxides of manganese and 

 the water, it is obvious, from the quotients in column (2) that 

 the composition of the ore is very accurately represented by 

 the formula Mua O3, HO + 3 Mn Oj, or that it is a compound of 

 one atom of manganite and three of pyvolusite. In the psi- 

 lomelanite analysed by Turner, there were 4 atoms of ses- 

 quioxide to 15 of peroxide; in that analysed by Berthier, 3 

 of sesquioxide to 17 of peroxide. It is obvious, therefore. 



