Berthierite

Berthierite – FeSb2S4
Elements: Iron, Antimony, Sulfur
Class: Sulfides
Crystal System: Orthorhombic
Hardness: 2-3
Calcite
Talc (1)Diamond (10)
Soft. A fingernail can scratch it.
Origin: Herja Mine, Chiuzbaia, Baia Mare, Marmures – Romania
Did you know?

Berthierite forms steel-gray needles almost identical to stibnite. The old way to tell them apart was fire: roasted, berthierite's hidden iron turns the stone magnetic, while stibnite stays inert.