Halite , Picromerite Locality: Potash Mine, Roßleben , Querfurt , Saxony-Anhalt , Germany ( Locality at mindat.org ) Size: miniature, 5.7 x 4.5 x 3.6 cm Picromerite (Schonite) on Halite A sharply crystallized example of this rare sulfate species, formerly known as Schonite, from a classic locality long abandoned. Minor halite is associated underneath and around the backside. It is, overall, a very attractive miniature. It carries an old label from the Bergakadmemie Freiberg. Sharp and complete all around, very 3-dimensional. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Picromerite
A hydrated potassium-magnesium sulfate — 'schoenite' — of marine salt deposits.
Intro adapted from Wikipedia (CC BY-SA).
Picromerite is an IMA-recognized mineral species in the sulfate class, with the chemical formula K₂Mg(SO₄)₂·6H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/a). It is a member of the Picromerite structural group.
Key properties: Mohs hardness 2.5; specific gravity 2.028; Vitreous luster; optically biaxial.
IMA symbol Pmr, IMA status: approved, named in 1955.
Principally occurs in oceanic bedded salt deposits; a volcanic sublimate in fumaroles; in a sulfate-rich hydrothermal ore deposit.
It is found associated with Halite, anhydrite, kainite, epsomite (oceanic salt deposits); hohmannite, metavoltine, metasideronatrite (Chuquicamata, Chile).
Its name comes from the Greek for bitter and part, in allusion to the magnesium in its composition.