A rich cluster of magnesioferrite crystals, intensely black with a metallic luster, exhibiting octahedral forms and rounded edges. They are accompanied on the calcite/dolomite matrix by litharge, which appears as an orange to reddish microcrystalline powder. This mineral, which forms a series with magnetite, is strongly magnetic.

This mineral species was first identified in Bergen Hill, New Jersey (USA). Stevensite is a rare phyllosilicate of the smectite group, with the formula (Ca,Na)xMg₃-x(Si₄O₁₀)(OH)₂. With black todorokite. This is an early specimen from Långban, Sweden. A systematic curiosity acquired from Shannon by E. Nicolau (Barcelona).

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