138 Mr HAI DIGGER'S Mineralogical Account of 



observed, and propose to give an account of, on some future oc- 

 casion. 



Pyrolusite was found by M. GMELIN to be a superoxide of 

 manganese. In most mineralogical works, the descriptions given 

 of the only species that they contain, is made up of the forms 

 and colour of manganite ; and the hardness, streak and colour of 

 pyrolusite. 



This is at once the most common species, and the most useful 

 one, on account of the large quantity of oxygen which it contains. 

 It is the ore of manganese properly so called, in an economical 

 point of view, and is extensively, though not exclusively, worked 

 for in many countries. The principal mines are the ancient ones 

 of Ilmenau, Friedricksroda, Reinwege, Elgersburg and other 

 places in Thuringia. Almost every one of the varieties, particu- 

 larly the compound ones, granular and columnar, are found there, 

 consisting of individuals of all sizes. Here, at Oehrenstock, near 

 Ilmenau, are also found the curious shapes of a parasitic forma- 

 tion, which present even the slightest peculiarities of the crystal- 

 lizations of calcareous spar as to regular form, but consist of a 

 tissue of crystals of pyrolusite, and engaged in a mass of the same 

 description. From the mines of Ehrensdorf near Maehrisch Trie- 

 bau in Moravia, since their discovery in 1798, many thousand 

 hundred weights of excellent ore are annually procured. At 

 Ehrensdorf the pyrolusite occurs in large nodules or masses, I 

 could not learn in what rock. It resembles the Thuringian va- 

 rieties. In Thuringia it forms veins in porphyry, and is often 

 accompanied with heavy spar. It is remarkable that no pyro- 

 lusite should have been found at Ihlefeld in the Hartz ; at least 

 there was no trace of it in all those collections which I examined, 

 if we except some thin masses in porphyry, and slender crystals, 

 evidently of the form of manganite, the superficial layers of 

 which yield a black streak, a circumstance which has not jet 

 received a satisfactory explanation. 



