transparent gypsum satin spar


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a semi-transparent gypsum satin spar specimen – see gallery

Mineral Group  sulphate
Composition  CaSO4.H2O
dimension (cm)  4.5×4.5×1.5
weight (g)  172

Gypsum has been known since antiquity. The 4th century BC Greek sculptor Lysippus of Sicyon was the first to use plaster manufactured from it. According to Pliny the Elder, he made the very first plaster cast of a human face.

This was probably the first mineral to be studied under the microscope in 1695 by Anton van Leeuwenhoek, a Dutch natural scientist, originally a merchant in Delft and the founder of microscopy.
It forms tabular or columnar crystals. The tabular crystals resemble mica (`Maria glass’). When pure, crystalline gypsum is clear and massive gypsum is white. Most frequently, however, it is tainted yellow or brown, according to the admixtures present. When finely granular it is called alabaster; when it is fibrous, it is called selenite. The name alabaster was derived from the Greek alabastros and is said to originate from the name of the Egyptian town Alabastron. The name selenite is also as old as the mineral classification system itself Intergrown gypsum crystals often form ‘swallow tails’; they also become rounded to a lenticular shape or gather to form star-shaped agglomerates. It can be scratched with a fingernail, by which it is distinguishable from similar minerals.
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Additional information

Weight 172 g
Dimensions 4.5 x 4.5 x 1.5 cm