This is a thumbnail size specimen 30 mm tall, Hydrodresserite is much rarer than Dresserite — Photo: Suolunite · CC BY-SA 4.0
Hydrodresserite
Hydrodresserite is an IMA-recognized mineral species in the carbonate class, with the chemical formula BaAl₂(CO₃)₂(OH)₄·3H₂O.
It crystallizes in the triclinic crystal system (space group P-1). It is a member of the Dundasite structural group.
Key properties: Mohs hardness 3–4; specific gravity 2.8; White streak; Vitreous luster; optically biaxial.
IMA symbol Hdrs, IMA status: approved, named in 1976.
Very rare, in vugs in metamorphosed limestone, near the contact zone of a dawsonite-rich silicocarbonatite sill.
It is found associated with Dresserite, weloganite, quartz.
The name refers to essential water and characteristic dehydration to dresserite under low humidity conditions.