Tincalconite

Tincalconite is a mineral closely related to borax, and is a secondary mineral that forms if borax is allowed to dry. The crystal shape of borax does not change during the drying process. Its formula is Na₂B₄O₅(OH)₄ – 3H₂O or Na₂B₄O₇ – 5H₂O.

While most tincalconite is created by man through exposing borax to dry air, there are natural occurrences of tincalconite, like in Searles Lake, California.