Telluride, marcasite group, cobalt-bearing mineral, forms a series with frohbergite
Common impurities: Fe,Sb
At the type locality, the Mattagami Lake mine, Matagami, Nord-du-Québec, Québec, Canada, mattagamite occurs in a small zone of telluride ore. The gangue is generally very rich in talc although chlorite in place of talc is present in some specimens. Magnetite and altaite are common ore minerals in the telluride zone and sphalerite and chalcopyrite are abundant in some specimens. Other minerals that are present include cobaltite, pyrrhotite, pyrite, hessite, tellurantimony and mattagamite.
Mattagamite was found in only one specimen, which contained fairly abundant sphalerite and chalcopyrite. It occurs as grains isolated in altaite, and as irregular rims on pyrrhotite and chalcopyrite in contact with altaite. Hessite is sometimes associated with the mattagamite rims (CM 12.55-60).
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