Specific gravity: 2.664
Hardness: 2½ to 3
Colour: Colourless, light grey, light brown; colourless in transmitted light
Solubility: Soluble in water
Melting point: 883oC
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
or just crumbled to powder.
At Boron, Kramer district, Kern county, California, USA, thénardite pseudomorphs after mirabilite form as dehydration products (KL p187).
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