Inderborite is a very rare borate mineral that is rarely available as being a gem that is faceted. It was discovered in 1940 at the Inder borate deposit, Kazakhstan. It is certainly one of those gems that are unusual are water soluble.

The main source of Inderborite crystals (and the locality that is type is from the Inder borate deposit, Kazakhstan. Other locations consist of Sarikaya, near Kirka, Eskiçehir Province, Turkey; the Günevi mine, Bigadiç borate district, Balikesir Province, Turkey; the Furnace Creek district, Death Valley, Inyo County, Ca, USA; the Santa Rosa mine, Sijes district, Salta Province, Argentina.

Chemical Formula:  CaMg[B3O3(OH)5]2•6(H2O)
Crystallography: Monoclinic – Prismatic
Crystal Habit: As well-formed prismatic crystals, to 10 cm, with a dozen forms noted; coarsely crystalline aggregates.
Twinning: None


Cleavage: [100] Good
Fracture: Conchoidal
Tenacity: Brittle
Hardness (Mohs): 3.5
Density: 1.93 – 2.00 (g/cm3)
Luminescence: None
Radioactivity: Not Radioactive
Other: Slowly soluble in cold water. Rapidly soluble in hot HCl.


Color: Colorless to White
Transparency: Transparent
Luster: Vitreous
Refractive Index: 1.482 – 1.540  Biaxial ( – )
Birefringence: 0.0480
Dispersion: None
Pleochroism: None