Not all interesting minerals are pretty. This is Pyrolusite from Norilsk. Norilsk is well known as ultrabasic massif, but
when the magma came in contact with limestone a skarn was also formed. This is a sample from that skarn.
The Manganese came from the magma, where there are other Mn minerals like Alabandite and Mn-Shadlunite.
[photo/collection: Maurice de Graaf]