• Chemistry: Na2B4O7 - 5H2 O, Hydrated Sodium Borate.
  • Class: Carbonates
  • Subclass: Borates
  • Uses: As an ore of boron and as a source of borax (a cleaning agent and useful industrial chemical)
  • Specimens

Tincalconite is a mineral that is closely related to and often intimately associated with the mineral borax. Most old mineral specimens of borax are chalky white due to a chemical reaction from dehydration. They have actually altered (at least on their surface and ultimately throughout) to the mineral tincalconite with the loss of water molecules. This kind of alteration from one mineral to another, can leave the shape of the original crystal intact. Mineralogists refer to this as a pseudomorph, or "false shape", because the tincalconite has the crystal shape of the predeceasing borax. Most all specimens of borax in museums and collections should technically be labeled "Tincalconite" or even more accurately "Tincalconite after Borax".

The formula of tincalconite can be written as: Na2B4O5(OH)4 - 3H2 O. This formula is technically identical to the formula that is generally used for tincalconite, Na2B4O7 - 5H2 O. The difference is in the number of oxygens, hydroxides and water molecules as shown below:

O2 + 2H2 O = (OH)4
The alternative formula reflects the ionic interaction of the hydroxides in the structure as opposed to a more passive role for the unbonded water molecules. The basic structure of tincalconite contains chains of interlocking BO2(OH) triangles and BO3(OH) tetrahedrons bonded to chains of sodium and water octahedrons.

Minerals that are the result of human intervention are sometimes not considered true minerals by mineral purists. Tincalconite, however, is not exclusively an alteration product of borax dehydration after the borax has been excavated, as some texts may lead people to believe. The mineral has been found as a naturally occurring secondary mineral at Searles Lake, California, the mineral's type locality. These specimens of cryptocrystalline aggregates are the result of dehydration of borax crystals that had been exposed to the dry air conditions at the site. In addition though, primary tincalconite crystals have been discovered there in drill cores forming well shaped di-rhombohedral pseudo-octahedral crystals. Primary means that the crystals were not the result of the alteration of other minerals.


  • Color is white.
  • Luster is dull to earthy.
  • Transparency: Specimens are translucent to dull.
  • Crystal System is trigonal.
  • Crystal Habits include cryptocrystalline aggregates and as crusts. Rare primary, di-rhombohedral, pseudo-octahedral crystals have been found in drill cores from Searles Lake, California. Pseudomorphs of borax are blocky to prismatic crystals with a nearly square cross section.
  • Cleavage is not seen.
  • Fracture is earthy.
  • Hardness is probably about 1.
  • Specific Gravity is approximately 1.8 - 1.9 (very light)
  • Streak is white.
  • Associated Minerals are calcite, halite, hanksite, colemanite, ulexite and other borates especially borax.
  • Other Characteristics: A sweet alkaline taste and further dehydration may cause crumbling.
  • Notable Occurrences include Trona, Boron, Death Valley; Searles Lake, San Bernardino County and other California localities; arid regions of the Andes Mountains, South America; Turkey and Tibet.
  • Best Field Indicators are pseudomorphing habit, color, associations, locality, density and hardness.
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TINCALCONITE specimen tin-1
$ 90.00
Dims: 4.8 x 4.4 x 3.5" (12.2 x 11.3 x 8.9 cm)
Wt: 13.1 oz. (370 g)
Baker Mine, Boron, California, U.S.A.
This large cabinet specimen consists of a cluster of several large Tincalconite pseudomorphs that extend from a crystalline Tincalconite base. These crystals are in excellent condition, showing little damage, and reach lengths of 2.4" (6 cm). Their excellent triclinic came from the borax from which they pseudomorphed. All have the classic white color, dull luster and opacity of their species.
no photo
tin-1 ($ 90.00)
Baker Mine, Boron, California, U.S.A.
TINCALCONITE specimen tin-2
$ 36.00
Dims: 2.4 x 0.6 x 0.5" (6.0 x 1.6 x 1.3 cm)
Wt: 15 g
Boron, California, U.S.A.
This single Tincalconite crystal is in excellent condition, showing almost no damage, and has very good monoclinic prismatic form that it retained through it pseudomorph from borax. It has the standard bright, white coloration and dull luster, and is essentially opaque. There is no base or host material present.
no photo
tin-2 ($ 36.00)
Boron, California, U.S.A.
TINCALCONITE specimen tin-3
$ 90.00
Dims: 5.2 x 4.9 x 3.2" (13.1 x 12.3 x 8.1 cm)
Wt: 13.8 oz. (391 g)
Baker Mine, Boron, Kern County, California, U.S.A.
Scores of intersecting Tincalconite crystals make up this cabinet specimen. The largest of these extend about 3" (7.5 cm) in length and measure about 0.8" (2 cm) in width and thickness. They are generally in good condition, though several are lightly damaged and a few are broken, and their monoclinic prismatic form is very good. The Tincalconite has the classic bright white coloration and dull luster of its species, and likely comprises a thick layer of material that surrounds a borax core in each crystal. There is no host rock present.
no photo
tin-3 ($ 90.00)
Baker Mine, Boron, Kern County, California, U.S.A.
TINCALCONITE specimen tin-4
$ 36.00
Dims: 2.7 x 0.5 x 0.5" (6.9 x 1.4 x 1.3 cm)
Wt: 14 g
Boron, Kern County, California, U.S.A.
This specimen consists of a single "crystal" of Tincalconite. The Tincalconite itself is probably only made up of a layer of powdery, white material around a core of crystalline borax- actually, it pseudomorphed from the borax through dehydration and has no crystal form of its own, retaining the monoclinic form of the borax. There is no base or host rock present.
no photo
tin-4 ($ 36.00)
Boron, Kern County, California, U.S.A.
TINCALCONITE specimen tin-5
$ 45.00
Dims:4.8x3.4x1.3" (12.2x8.6x3.3 cm)
Wt: 10.4oz. (296g)
Baker Mine, Boron, California
This specimen consists of a large, chalk-white mass of tincalconite crystals. These crystals are actually pseudomorphs of tincalconite after borax. It displays a powdwery texture and a dull luster. There is only minor damage to this specimen.
no photo
tin-5 ($ 45.00)
Baker Mine, Boron, California


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