6 Photos
Tincalconite
Chemical Formula	Na2[B4O5(OH)4]·3H2O
Species	Borates
Crystal System	Trigonal
Mohs Scale	2
Specific Gravity	1.88
Color	White, colourless (artificial material); colourless in transmitted light.
Luster	Vitreous, Dull
Refractive Index	n = 1.461 n = 1.474
Diaphaneity	Transparent, Translucent
Fracture	Hackly
Crystal Habit：Fine-grained powder. Artificial crystals pseudo-cubic with equal development of the commonest forms "r" and "c," yielding an octahedron-like habit.

Tincalconite is a hydrous sodium borate mineral closely related to borax, and is a secondary mineral that forms as a dehydration product of borax. Its formula is Na₂B₄O₇·5H₂O or Na₂[B₄O₅(OH)₄]·3H₂O.

Tincalconite typically occurs as a fine grained white powder. It crystallizes in the hexagonal crystal system and has been found as primary euhedral di-rhombohedral, pseudo-octahedral crystals. It is also found pseudomorphically replacing borax crystals. It has a specific gravity of 1.88 and a Mohs hardness of 2. Refractive index values are nω=1.460 and nε=1.470.

While most tincalconite is created by man through exposing borax to dry air, there are natural occurrences of tincalconite, as in Searles Lake, California where it was first described in 1878. In addition to several California and Nevada locations it is reported from Argentina, Italy, Turkey and Ukraine.

The name comes from "tincal", Sanskrit for borax, and Greek, "konis", meaning powder, for its composition and typical powdery nature.