White single crystals of the rare borate mineral rivadavite from the type locality in Argentina and only one of the three known localities worlwide (Tincalayu Mine, Salar Del Hombre Muerto, Los Andes, Salta, Argentina). Ex Vandenbroucke Museum collection specimen, from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Rivadavite
Rivadavite is an IMA-recognized mineral species in the borate class, with the chemical formula Na₆Mg[B₆O₇(OH)₆]₄·10H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/m).
Key properties: Mohs hardness 3.5; specific gravity 1.905; Vitreous, silky in aggregates luster; optically biaxial.
IMA symbol Riv, IMA status: approved, named in 1966.
Found in sedimentary borate deposits; deposited from borate-rich hot springs.
It is found associated with Borax, tincalconite (Tincalayu deposit, Argentina).
In honor of Bernardino Rivadavia (1780–1845), first President of the Argentine Republic.