Outstanding colorless crystals of the very rare mineral Na-Ca sulphate mineral cesanite from the TL in Cesane (Cesano 1 Well, Cesano, Rome Province, Lazio, Italy). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Cesanite
The sulfate end-member of the apatite-wilkeite-ellestadite series, with sulfate and sodium swapped in for phosphate and calcium.
Intro adapted from Wikipedia (CC BY-SA).
Cesanite is an IMA-recognized mineral species in the sulfate class, with the chemical formula Ca₂Na₃(SO₄)₃OH.
It crystallizes in the hexagonal crystal system (space group P6_3/m). It is a member of the Apatite structural group.
Key properties: Mohs hardness 2–3; specific gravity 2.786; Greasy to silky in aggregates luster; refractive index 1.567; optically uniaxial.
IMA symbol Csa, IMA status: approved, named in 1980.
Occurs as vein and cavity fillings in brecciated rock in an active geothermal field.
It is found associated with Görgeyite, pyrite, gypsum, anhydrite, aphthitalite, kalistrontite, glauberite.
The name is derived from the locality near Cesano, Italy.