Mirabilite

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Mirabilite
Mineralogical name	Mirabilite
Chemical name	Sodiumsulfate decahydrate
Trivial name	Glauber salt, Reussin, Sulphate of Soda
Chemical formula	Na2SO4•10H2O
Other forms	Sodiumsulphate heptahydrate Na2SO4•7H2O
Crystal system	monoclinic
Crystal structure
Deliquescence humidity 20°C	93.6% (20°C), 90% (23°C), 87% (25°C)
Solubility (g/l) at 20°C	900 g/l
Density (g/cm³)	1.464 g/cm³
Molar volume	219.8 cm3/mol
Molar weight	322.21 g/mol
Transparency	transparent to opaque
Cleavage	perfect
Crystal habit
Twinning
Phase transition
Chemical behavior
Comments	soluble in water and glycerin, not soluble in pure alcohol easily loses some water, converts to thenardite at 32°C anormal blue or brown interference colours
Crystal Optics
Refractive Indices	nx = 1.395 ny = 1.396-1.410 nz = 1.398-1.419
Birefringence	Δ = 0.04-0.023
Optical Orientation	negative
Pleochroism
Dispersion
Used Literature
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Solubility properties

Figure1: Solubility of thenardite and mirabilite compared with other salts[after [Stark.etal:1996]Title: Bauschädliche Salze
Author: Stark, Jochen; Stürmer, Sylvia
].

Under the polarising microscope

• Sodium sulfate crytallisation between two glas slides
• 

  Photo taken with crossed polarisers and red I

• 

  Photo taken with crossed polarisers

Literatur

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A phase is a physically distinctive form of matter and is characterized by having relatively uniform chemical and physical properties.

In physics, interference is the addition of two or more waves that results in a new wave pattern. The colours are produced by the difference in speed in the fast and slow rays. Minerals have specific and predictable colours in cross-polarized light, and this can help identify them.