Yellow crystal aggregates of the rare mineral betpakdalite, probably betpakdalite-CaCa. First German find of these rare species. From: Sadisdorf, Ezgebirge, Saxony, Germany. — Photo: David Hospital · CC BY-SA 4.0
Betpakdalite-CaCa
Betpakdalite-CaCa is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula [Ca₂(H₂O)₁₇Ca(H₂O)₆][Mo⁶⁺₈As⁵⁺₂Fe³⁺₃O₃₆(OH)].
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Betpakdalite structural group.
Key properties: Mohs hardness 3; specific gravity 2.98–3.05; Dull to waxy luster; optically biaxial.
IMA symbol Bpd-CaCa, IMA status: approved, named in 1961.
Filling cracks in leached pyrite in the oxidized zone of a mineral deposit (Kara-Oba deposit, Kazakhstan); on vein quartz (Krupka, Czech Republic).
It is found associated with Ferrimolybdite, gypsum, jarosite, hydromica, “limonite”, “opal” (Kara-Oba deposit, Kazakhstan); molybdenite, molybdite, quartz (Krupka, Czech Republic).
The name refers to the original occurrence in the Bet-Pak-Dal Desert, Kazakhstan. Two suffixes correspond to the dominant cations in the two different types of non-framework cation sites.