or Prismatic Manganese Ore. 305 



from the brown and green tints produced by carbonaceous 

 matter and protoxide of iron. The manganese of commerce 

 has been for this reason facetiously called by the French le 

 savon des verriers, or le savon du verre. 



There can be no doubt that pyrolusite should form a species 

 of its own, if we only attend to the marked differences in its 

 hardness, strength, &c. from all the rest. As yet, however, its 

 regular forms are unknown. For some time past I have endea- 

 voured to collect specimens either of crystals or cleavable mas- 

 ses of this substance, but have not succeeded in getting any 

 fit for measurement. Mr Von Leonhard kindly communicated 

 to me some crystals from Tiefe Kohlenbach, near Eiserfeld, 

 in the province of Siegen, possessing the form (Plate IV. 

 Fig. 5,) with uneven surfaces, and yielding a black streak. 

 They form a coating on the reniform shapes of the uncleav- 

 able manganese-ore, or Psilomelane. Professor Gustavus 

 Rose had obtained a similar specimen from the same source ; 

 and by some approximate measurements, but which were far 

 from decisive, we found the inclination of a on a, over the 

 small face b, to be = 86° 20'. The faces of the horizontal 

 prism d, did not admit of measurement at all. There exists 

 cleavage parallel to a and b, but not very perfect. Among 

 the forms of Prism atoidal Manganese-Ore, (or Manganite,) 

 there is no prism, parallel to the axis, which even comes near 

 the one here mentioned, though the approximation at the 

 angles be ever so rude ; and the crystals may be therefore 

 considered as the actual type of the species of pyrolusite, 

 which is likewise the opinion of Mr Rose. I have observed 

 crystals of the form of manganite, yielding the characteristic 

 brown streak only in the interior portions of the crystals, 

 while that of the exterior strata is black. This may be the 

 result of one of those changes of substance, the form remain- 

 ing the same, which are recorded in a preceding part of this 

 volume. It may, however, be also one of those curious in- 

 stances, where two species, of different forms, enter, as it were, 

 into a regular composition with each other, as in felspar and 

 albite, disthene and staurolite, and others ; many of which I 

 have observed* and propose to give an account of, on some 

 future occasion. 



