Tincalconite. Collected by Jim Minette from Boron Open Pit, Boron, California. Mineral collection of Bringham Young University Department of Geology, Provo, Utah. Photograph by Andrew Silver. BYU index 8- 1015, Na_2B_4O_5(OH)_4 - 3H_2O. — Photo: Andrew Silver, USGS · Public domain
Tincalconite
A hydrated sodium borate — 'octahedral borax' — formed when borax dehydrates.
Intro adapted from Wikipedia (CC BY-SA).
Tincalconite is an IMA-recognized mineral species in the borate class, with the chemical formula Na₂B₄O₅(OH)₄·3H₂O.
It crystallizes in the hexagonal crystal system (space group R32).
Key properties: specific gravity 1.88; Vitreous to dull luster; optically uniaxial.
IMA symbol Tnc, grandfathered status — known before the IMA’s founding, named in 1878.
Typically a dehydration product of other borates.
It is found associated with Borax, kernite.
The name comes from tincal, an Oriental name for borax, and the Greek for powder, in allusion to the typical powdery habit.