pirssonite

from The Century Dictionary.

• noun A hydrated carbonate of calcium and sodium, CaCO₃.Na₂CO₃+2H₂O, occurring in colorless or white prismatic crystals: found at Borax Lake, California.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun mineralogy a saline evaporite, consisting of a mixed sodium and calcium carbonate