Leonard James Spencer, 1911 Encyclopædia Britannica, Volume 7… (1911)
“ The mineral also occurs as compact masses of considerable extent. The colour is dark lead-grey with a metallic lustre, but this is never very bright, since the material is readily altered, becoming black and dull on exposure to light. The mineral is soft (H.=21⁄2) and sectile, and can be readily cut with a knife, like argentite ”
