Dr. Turner on a Specimen of Varx)icite from Ihlefeld. 285 



lime, which has been afterwards removed and carbonate of 

 manganese substituted, by the action of carbonated springs 

 holding the latter salt in solution ; or, since carbonate of man- 

 ganese is isomorphous with carbonate of lime, the former may 

 possibly have assumed the pyramidal form in which calcareous 

 spar sometimes occurs, by dii'ect crystallization. However 

 this may be, the crystals in my specimen are quite free from 

 carbonate of lime, and contain, besides oxide of manganese, 

 nothing but traces of baryta and oxide of iron. 



The mineral is made up of small lamellated prismatic cry- 

 stals, too confusedly intermixed to admit of an accurate deter- 

 mination of cleavage, but in lustre and general outline resem- 

 bling varvicite and manganite. The colour of its streak and 

 powder is like that of varvicite, and in hardness also it corre- 

 sponds with that mineral. Its specific gravity is 4.623, while 

 that of varvicite is 4"531. When converted into red oxide by 

 a white heat, it loses 13'13 per cent, of which 4'98 are water 

 and 8'15 oxygen ; whereas your varvicite under the same cir- 

 cumstances loses 13*11 per cent, of which 5"725 are water, 

 and 7*38 5 oxygen. 



It appears to me from these characters that the mineral 

 under examination must either be varvicite with a small ad- 

 mixture of peroxide, or a mixture of peroxide with a consi- 

 derable quantity of manganite. But the last supposition is un- 

 tenable; since a mixture of crystalline particles of such unequal 

 hardness as manganite and the peroxide, could not fail to be 

 recognised as such ; while this mineral, throughout, is of uni- 

 form hardness. 



It may not be useless, while writing on the subject of man- 

 ganese, to state a fact which I do not remember to have seen 

 noticed by others. When chemists, in preparing pure salts 

 of manganese, add oxalate of ammonia or potash to a solution 

 of the chloride, and the liquid retains its transparency, it is 

 usual to infer the total absence of lime. But the inference is 

 not altogether correct; for the solution of chloride of manga- 

 nese, though perfectly neutral, gives to oxalate of lime a de- 

 gree of solubility which that salt does not possess in pure water. 

 Hence I have known a solution of manganese to retain its trans- 

 parency an hour or two after oxalate of ammonia was added, 

 but to deposit a little oxalate of lime in the course of twenty-four 

 hours ; and when, after that period, the clear liquid was preci- 

 pitated by an alkaline carbonate, tlie carbonate of manganese 

 taken up in nitric acid, and the nitrate decomposed by a heat 

 sliort of redness, the residue yielded nitrate of lime to water. 

 I am, dear Sir, yours very truly, 



Uiiivcibit)' of London, March loth, 1830. Edw. Turner. 



XLII. Results 



