**1.2 Anhydrite: CaSO4**

crystal system: orthorhombic; hardness: 3.5, density: 2.98 g/cm2 hardly soluble in: HCl and concentrated H2SO4 contains impurities: Ba, Sr

habit: platy, columnar, fibrous; the crystal size rarely exceeds 0.5-1 mm (fig. 11.); sometimes crystals grown in caverns and fractures appear; massive aggregates (fig. 13.), rare radiant aggregates exceptionally reach the length of few cm

usually colourless crystals

particular varieties:


Fig. 5. Selenite (Busko-Zdrój, Poland) phot. J. Jaworska

**1.2 Anhydrite: CaSO4**

contains impurities: Ba, Sr

usually colourless crystals particular varieties: - enterolithic anhydrite

Fig. 6. Gypsum twins – swallowtail (Dymaczewo Stare, Poland) phot. J. Jaworska

habit: platy, columnar, fibrous; the crystal size rarely exceeds 0.5-1 mm (fig. 11.); sometimes crystals grown in caverns and fractures appear; massive aggregates (fig. 13.), rare radiant


crystal system: orthorhombic; hardness: 3.5, density: 2.98 g/cm2

hardly soluble in: HCl and concentrated H2SO4

aggregates exceptionally reach the length of few cm

Recently, the gypsum precipitates from among calcium sulphates; whereas anhydrite crystallizes very rarely – the only locations of its recent crystallization are: the Persian Gulf coast, lakes: Elton and Inger, Death Valley and Clayton Playa (Nevada).

Fig. 7. Fibrous –spar gypsum in clay-slate (Niwnice, Poland) phot. J. Jaworska

Fig. 8. Desert rose; phot. J. Jaworska

Fig. 9. Biolaminas deformed by crystallizing sulphates (near Ostrówka quarry, Poland) phot. J. Jaworska

Crystallization, Alternation and Recrystallization of Sulphates 471

Fig. 13. Anhydrite rock - massie agreggates (Niwnice, Poland) phot. J. Jaworska

Fig. 14. Sabre-like gypsum (Nida region, Poland) phot. J. Jaworska

Fig. 15. Laminated gypsum (Niemeyer quarry, Germany) phot. J. Jaworska

mineral (fig. 21.).

salinity and in temperature about 40°C). Not until the concentration of solution reaches values close to NaCl concentration, the only phase of calcium sulphate which crystallizes and accompanies the rock salts is anhydrite; even if the temperature does not exceed 18°C. The thick rock salt deposits seldom form salt pillows together with salt swells and diapirs; their roof surfaces are located close to the Earth's surface (at the boundary of the salt mirror) and easily undergo leaching, leaving less soluble residue of - among the others - anhydrite grains and next - the anhydrite sandstone (fig. 20.), forming so-called cap-rock that forms the natural cover of the salt deposit. The anhydrite sandstone can – depending on the conditions - undergo further transformation typical for this very

Fig. 10. Lenticular gypsum (Wapno cap-rock, Poland) phot. J. Jaworska

Fig. 11. Anhydrite crystals (from Dębina salt dome, Poland), phot. A. Kyc

12. Enterolithic anhydrite (Wieliczka mine, Poland) phot. J. Jaworska
