White crystals of the very rare Na borate-carbonate mineral qilianshanite from one of only three known localities worldwide (Alkali Lake, Lake County, Oregon, United States of America) and associated to nahcolite. Ex. Erich Laskowski collection (USA). — Photo: David Hospital · CC BY 4.0
Qilianshanite
Qilianshanite is an IMA-recognized mineral species in the borate class, with the chemical formula NaH₄(CO₃)(BO₃)·2H₂O.
It crystallizes in the monoclinic crystal system (space group C2).
Key properties: Mohs hardness 2; specific gravity 1.706; White streak; Vitreous luster; optically biaxial.
IMA symbol Qil, IMA status: approved, named in 1992.
Formed by reaction of borate-rich waters with earlier sodium carbonates in a borate deposit.
It is found associated with Tincalconite, nahcolite, calcite, quartz.
The name refers to its occurrence in the Qilian Mountains, China.