nSternbergite(Min) A sulphide of silver and iron, occurring in soft flexible laminæ varying in color from brown to black.
Century Dictionary and Cyclopedia
nsternbergiteAn ore of silver, a sulphid of silver and iron, having a pinchbeck-brown color and metallic luster. It occurs foliated, the laminæ being soft and flexible. It leaves a mark on paper like that of graphite.