Outstanding yellow crystals of the rare arsenic sulphide mineral dimorphite from the TL in Italy (Solfatara di Pozzuoli, Phlegrean Fields, Naples Province, Campania, Italy) and one of the very few known localities worldiwde. Ex. Erich Laskowski collection (USA) — Photo: David Hospital · CC BY 4.0
Dimorphite
A very rare orange-yellow arsenic sulfide (As₄S₃) deposited by volcanic fumaroles at 70–80 °C.
Intro adapted from Wikipedia (CC BY-SA).
Dimorphite is an IMA-recognized mineral species in the sulfide class, with the chemical formula As₄S₃.
It crystallizes in the orthorhombic crystal system (space group Pnma).
Key properties: Mohs hardness 1.5; specific gravity 3.58; Adamantine. R1 –R2: n.d luster.
IMA symbol Dim, grandfathered status — known before the IMA’s founding, named in 1849.
Deposited at a fumerolic vent at temperatures of about 70 ° C–80 ° C (Solfatara, Italy); formed in an ore deposit under secondary conditions (Chile).
It is found associated with Realgar, sal ammoniac, sulfur, various sulfates (Solfatara, Italy); orpiment (Chile).
Its name comes from the Greek for two and form, in reference to the two forms in which the species was thought to occur.