Outstanding white crystals of the extremely rare Ba-Na silicoborate mineral garrelsite from the TL (South Ouray No 1 Well, Ouray, Uintah County, Utah, United States of America) and only one of the two known localities worldwide in a black contrasting matrix. Recovered from a drill core from a depth of 2185 feet. Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY 4.0
Garrelsite
Garrelsite is an IMA-recognized mineral species in the silicate class, with the chemical formula NaBa₃B₇Si₂O₁₆(OH)₄.
It crystallizes in the monoclinic crystal system (space group C2/c).
Key properties: Mohs hardness 6; specific gravity 3.68; White streak; Vitreous luster; optically biaxial.
IMA symbol Grr, grandfathered status — known before the IMA’s founding, named in 1955.
Of authigenic origin, in dolomitic shale in drill core from the Green River Formation (Uintah Co., Utah, USA).
It is found associated with Nahcolite, shortite, searlesite, wurtzite (Uintah Co., Utah, USA).
The name refers to Professor Robert Minard Garrels (1916–1988), American geochemist and educator.