Outstanding yellow crystals of the very rare lead mineral trigonite from the type and only known locality worldwide, the famous Langban deposit. This is one of the most sought-after, well crystallized rarities from the famous Langban Mine in Sweden. The mineral was exclusively found within the so-called Hindenburg working of the mine. — Photo: David Hospital · CC BY-SA 4.0
Trigonite
Trigonite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Pb₃Mn²⁺(AsO₃)₂(AsO₂OH).
It crystallizes in the monoclinic crystal system (space group Pn).
Key properties: Mohs hardness 2–3; specific gravity 6.1–7.1; Vitreous to adamantine luster; optically biaxial.
IMA symbol Tgn, grandfathered status — known before the IMA’s founding, named in 1920.
Found in a metamorphosed Fe–Mn orebody.
It is found associated with Lead, dixenite, hausmannite, finnemanite, rouseite, dolomite, barite.
Its name comes from the Greek for triangle, alluding to the characteristic crystal outline.