Fontarnauite
A recently described hydrated sulfate-borate from evaporite boron deposits.
Intro adapted from Wikipedia (CC BY-SA).
Fontarnauite is an IMA-recognized mineral species in the borate class, with the chemical formula (Na,K)₂(Sr,Ca)(SO₄)[B₅O₈(OH)](H₂O)₂.
It crystallizes in the monoclinic crystal system (space group P2_1/c).
Key properties: Mohs hardness 2.5–3; specific gravity 2.37; White streak; Pearly luster; optically biaxial.
IMA symbol Fon, IMA status: approved, named in 2009.
An early diagenetic phase in borate-bearing marls and tuffs.
It is found associated with Probertite, glauberite, celestine; or with halite, kaliborite replacing probertite, kalistronite replacing fontarnauite in pseudomorphs after glauberite.
The mineral was named to honor Dr. Ramon Fontarnau i Griera, in recognition of his efforts to promote the development of scientific facilities focused on mineral characterization.