Hydroboracite Locality: Death Valley , Inyo County , California , USA ( Locality at mindat.org ) Size: 4.7 x 3.8 x 3.0 cm. Hydroboracite is a rare hydrated borate. This is a very fine specimen of diverging sprays of large, waxy lustre, blades nicely set in matrix. I like the way the largest spray is front and center, in the most prominent position. Old material from Death Valley. Rarely crystallized in such quality as you see here. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Hydroboracite
A hydrated calcium-magnesium borate discovered in 1834 at Kazakhstan's Inder lake.
Intro adapted from Wikipedia (CC BY-SA).
Hydroboracite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula CaMg[B₃O₄(OH)₃]₂·3H₂O.
It crystallizes in the monoclinic crystal system (space group P2/c).
Key properties: Mohs hardness 2–3; specific gravity 2.15–2.17; Vitreous, silky if fibrous luster; refractive index 1.542; optically biaxial.
IMA symbol Hbo, grandfathered status — known before the IMA’s founding, named in 1834.
Typically formed by groundwater alteration of colemanite; may be primary.
It is found associated with Colemanite, hydroboracite, tunellite.
In allusion to essential water and a supposed relation to boracite.