: a mineral consisting of ferruginous sphalerite that is dark brown to black in color
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marmatite Min.(ˈmɑːmətaɪt)
[a. G. marmatit, f. Marmato (S. Amer.).]
A ferriferous variety of sphalerite.
Penny Cycl. XXVII. 781/2.
Useful english dictionary. 2012.