Tincalconite is a hydrous sodium hydroxy-borate mineral (Na2B4O5(OH)43H2O).  It often forms as a result of dehydration (removal of some water) of other borate minerals, such as borax (Na2(B4O7)10H2O).  Tincalconite has a nonmetallic luster that is dull to glassy in some specimens.  It is quite soft (H=2) and has a white, powdery appearance.  It usually takes on the crystal form of the pre-alteration mineral.


Tincalconite taking on the crystal forms of the precursor mineral, borax (i.e., tincalconite pseudomorphs after borax).

Locality: Boron, southeastern Kern County, southern California, USA.

(CSM # 75.28, Colorado School of Mines Geology Museum, Golden, Colorado, USA)



Photo gallery of tincalconite



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