Formula: Na2(SO4) sulphate
Specific gravity: 2.664
Hardness: 2½ to 3
Streak: White
Colour: Colourless, light grey, light brown; colourless in transmitted light
Solubility: Soluble in water
Melting point: 883oC

Sedimentary environments
Volcanic sublimates and fumeroles

Thénardite occurs in non-marine evaporite deposits in arid climates or it is formed by alteration of alkali-igneous rocks protected from water. It may deposit from volcanic gas at volcanic vents. In evaporite deposits it may be associated with trona and tychite, and in fumeroles with aphthitalite. In dry air mirabilite dehydrates to form thénardite, either as pseudomorphs of thénardite after mirabilite, or just crumbled to powder.

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