Very big single crystal of the rare mineral Oxo-magnesio-hastingsite (IMA 2011-035, but approved in 2013) from the fourth locality worldwide: Dolánky, Ohníč, Teplice, Ústí Region, Bohemia, Czech Republic. — Photo: David Hospital · CC BY-SA 4.0
Oxo-magnesio-hastingsite
Oxo-magnesio-hastingsite is an IMA-recognized mineral species in the silicate class, with the chemical formula NaCa₂(Mg₂Fe³⁺₃)(Si₆Al₂)O₂₂O₂.
It crystallizes in the monoclinic crystal system (space group C2/m). It is a member of the Amphibole structural group.
Key properties: Mohs hardness 6; specific gravity 3.19; White streak; Vitreous luster; optically biaxial.
IMA symbol Omhst, IMA status: approved, named in 2011.
Occurs as reacted megacrysts in melilititic tuff derived from a silica-undersaturated alkaline magma.
It is found associated with Diopside, phlogopite.
As the oxygen- and magnesium- dominant analogue of hastingsite.