Gypsum^[1]^[2]

Mineralogical name	Gypsum, Selenite
Chemical name	Calcium sulfate dihydrate
Trivial name	Gypsite, Sulfate of Lime
Chemical formula	Ca[SO₄]•2H₂O
Other forms	Anhydrite (CaSO₄) Hemihydrate (CaSO₄•0.5H₂O)
Crystal system	monoclinic
Crystal structure
Deliquescence humidity 20°C
Solubility (g/l) at 20°C	2.14 g/l
Density (g/cm³)	2.2-2.4 g/cm³
Molar volume	74.69 cm³/mol
Molar weight	172.17g /mol
Transparency	transparent to opaque
Cleavage	perfect
Crystal habit
Twinning
Phase transition
Chemical behavior
Comments	hardly soluble in water
Crystal Optics
Refractive Indices	α = 1.519-1.521 β = 1.522-1.523 γ = 1.529-1.530
Birefringence	Δ = 0.010
Optical Orientation	biaxial positive
Pleochroism
Dispersion	58°
Used Literature
{{{Literature}}}

Authors: Hans-Jürgen Schwarz , Nils Mainusch, Tim Müller back to Sulfate

Calciumsulfate and Gipsum[edit]

Solubility properties[edit]

Figure1: Solubility of CaSO4 in water (diagram: Michael Steiger)

Figure 2:Solubility of gipsum compared with other salte (after [Stark.etal:1996]Title: Bauschädliche Salze
Author: Stark, Jochen; Stürmer, Sylvia

)

Photos of gypsum crystals and deterioration pattern caused by gypsum[edit]

On a object[edit]

salt damage on a brick, St. Jakobi Perleberg

Under the polarising microscope[edit]

In thin section of bricks
Brick with gypsum caused damage, St. Jakobi Perleberg
Brick with gypsum caused damage, St. Jakobi Perleberg

Gypsum crystallized out of a solution in water on a glass slide
Calcium sulfate crystallized out of a solution in water on a glass slide
Calcium sulfate with sodium chloride of a real sample, Gypsum crystallized out of a solution in water on a glass slide
Calcium sulfate with sodium chloride of a real sample, Gypsum crystallized out of a solution in water on a glass slide
Calcium sulfate, Gypsum crystallized out of a solution in water on a glass slide