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 Church, Perleberg

Under the polarising microscope[edit]

In thin section of bricks
Brick with gypsum caused damage, St. Jakobi Church, Perleberg, Germany
Brick with gypsum caused damage, St. Jakobi Church, Perleberg, Germany
Gypsum crystals between plaster layers

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