White crystals of haidingerite associated to yellow orpiment and red realgar. From: White Caps Mine, Manhattan District, Nevada, United States of America. — Photo: David Hospital · CC BY-SA 4.0
Haidingerite
A hydrated calcium hydrogen arsenate forming scaly and botryoidal orthorhombic coatings.
Intro adapted from Wikipedia (CC BY-SA).
Haidingerite is an IMA-recognized mineral species in the arsenate class, with the chemical formula Ca(AsO₃OH)·H₂O.
It crystallizes in the orthorhombic crystal system (space group Pcnb).
Key properties: Mohs hardness 2–2.5; specific gravity 2.85–2.96; Vitreous; pearly on cleavages luster; optically biaxial.
IMA symbol Hdi, grandfathered status — known before the IMA’s founding, named in 1827.
Formed by dehydration of pharmacolite (Getchell mine, Nevada, USA).
It is found associated with Pharmacolite, pitticite, weilite.
The mineral was named to honor Wilhelm Karl von Haidinger (1795–1871), Austrian mineralogist.