• Chemistry: CaMgB6O11 - 6H2O, Hydrated Calcium Magnesium Borate.
  • Class: Carbonates
  • Subclass: Borates
  • Uses: As a minor source of boron and as mineral specimens.
  • Specimens

Hydroboracite is an uncommon borate mineral. It is one of the borate minerals that form silky, fibrous crystal clusters. Ulexite is another more common borate that forms similar fibrous aggregates and thus the two minerals are not easy to distinguish. Hydroboracite's silky luster is quite attractive.


  • Color is colorless, white to brownish.
  • Luster is vitreous to silky.
  • Transparency: Specimens are translucent to transparent.
  • Crystal System is monoclinic.
  • Crystal Habits include acicular or fibrous radiating clusters and finely granular masses. Tiny crystals have a wedge-shaped termination.
  • Cleavage is perfect.
  • Fracture is uneven.
  • Hardness is 2 - 3
  • Specific Gravity is approximately 2.2 (below average)
  • Streak is white.
  • Associated Minerals are halite, anhydrite, tunellite, colemanite, ulexite and other borates especially borax.
  • Notable Occurrences include the type locality at Lake Inder, Caucasus Mountains in Southwest Asia; Harz Mountains, Germany; the Furnace Creek Formation of Inyo County and the Boron open-pit mine, Kern County, California, USA.
  • Best Field Indicators are crystal habit, associations, locality, luster and density.
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HYDROBORACITE specimen hyo-1
$ 48.00
Dims:2.1x0.9x0.6" (5.3x2.3x1.5 cm)
Wt: 0.4oz. (10g)
Bigadic, Turkey
This specimen consists of an intergrown cluster of fibrous hydroboracite crystals. This habit is common among Turkish specimens. The crystals show impurities in places (the darker colors), and are relativly undamaged. No details of the monoclinic crystal form can be observed. This specimen exhibits a pearly luster.
no photo
hyo-1 ($ 48.00)
Bigadic, Turkey
HYDROBORACITE specimen hyo-2
$ 72.00
Dims:1.6x1.5x0.7" (4.1x3.8x1.8 cm)
Wt: 0.5oz. (14g)
Thompson Mine, Ryan, Inyo cty., California
This is an excellent specimen of fibrous, radiating boracite crystals on a small amount of evaporite matrix. The crystals are translucent to transparent on the tips, and show good monoclinic terminations. A few of the crystals show some damage, but this is relatively minor. One side of the cluster shows minor iron staining.
no photo
hyo-2 ($ 72.00)
Thompson Mine, Ryan, Inyo cty., California
HYDROBORACITE specimen hyo-3
$ 48.00
Dims:1.3x1.1x0.9" (3.3x2.8x2.3 cm)
Wt: 0.5oz. (15g)
Mt. Blanco, Death Valley, Inyo cty., California
This is an interesting specimen. One side of the matrix of this piece is covered with sprays of acicular hydroboracite. The other side of the matrix is covered with blades of colemanite. The hydroboracite crystals reach 0.5" (1.3cm) in length; the colemanite crystals reach 0.2" (0.5cm) in length. There is only minor damage around the edges of this specimen.
no photo
hyo-3 ($ 48.00)
Mt. Blanco, Death Valley, Inyo cty., California


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