thermonatrite

{{Infobox mineral | name = Thermonatrite | image = Villiaumite5 - Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada.jpg | alt = | caption = Villiaumite and thermonatrite (powdery coating) | category = Carbonate mineral | formula = Na2CO3·H2O | IMAsymbol = Tnat | molweight = | strunz = 5.CB.05 | system = Orthorhombic | class = Pyramidal (mm2) H-M symbol: (mm2) | symmetry = Pca21 | unit cell = a = 10.72 Å, b = 5.24 Å c = 6.46 Å; Z = 4 | colour = Colourless to grey or yellow, white | habit = Acicular crystals rare; typically occurs as powdery crusts | twinning = | cleavage = Poor to indistinct on {100} | fracture = Sectile | tenacity = | mohs = 1 – | lustre = Vitreous | streak = | diaphaneity = Transparent | gravity = 2.255 (measured on synthetic crystal) | density = | polish = | opticalprop = Biaxial (−) | refractive = nα = 1.420 nβ = 1.506 nγ = 1.524 | birefringence = δ = 0.104 | pleochroism = | 2V = 48° (measured) | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = Soluble in water | impurities = | alteration = | other = Readily dehydrates | prop1 = | prop1text = | references = }}

Thermonatrite is a naturally occurring evaporite mineral form of sodium carbonate, Na2CO3·H2O.