Brass- yellow metallic crystal aggregtate of the very rare nickel selenide mineral sederholmite from the TL and only known locality worldwide in Finland: Kuusamo, North Ostrobothnia, Finland. Probably analyzed specimen by the former owner of the specimen (the Vandenbroucke Museum) since both sides of the specimen are polished, but the analysis is no longer available. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Sederholmite
Sederholmite is an IMA-recognized mineral species in the sulfide class, with the chemical formula NiSe.
It crystallizes in the hexagonal crystal system (space group P6_3mc). It is a member of the Nickeline structural group.
Key properties: specific gravity 7.06; optically uniaxial.
IMA symbol Sdh, IMA status: approved, named in 1964.
Found in calcite veins, in sills of albite diabase in schist, in association with low-grade uranium mineralization.
It is found associated with Wilkmanite, penroseite, clausthalite, calcite.
In honor of Jakob Johannes Sederholm (1863–1934), former Director of the Geological Survey of Finland.