Bassanite

Description

A naturally and synthetically occurring mineral composed of an intermediate (one-half) hydrate form of Calcium sulfate that lies between the dihydrate (Gypsum) and the anhydrous (Anhydrite) states. Natural particles of bassanite were first described in 1910 for an occurrence on Mount Vesuvius. Synthetic particles of bassanite occur when gypsum is calcined to form Plaster of Paris.

Physical and Chemical Properties

• Composition = CaSO4-¹/₂H2O
• Refractive Index = 1.55, 1.57
• Specific gravity = 2.69-2.76
• Microscopically similar to gypsum and plaster of Paris
• Luster = earthy
• Streak = white

Resources and Citations

• Wikipedia: Bassanite Accessed March 2025