Mercury(II) selenide, typically steel-grey to black. It's associated with deep transformation but is highly toxic due to mercury and selenium.
Steel-Grey, Blackish-Grey, Reddish-Brown (internal reflection), often massive or granular
Tiemannite is classified as a selenide mineral mineral which typically crystallizes in the isometric system. Its chemical formula is HgSe. Common crystal habits include massive and as euhedral crystals.