Afwillite is a rare calcium silicate hydrate mineral, typically found in metamorphosed limestones and sometimes in cement chemistry contexts. It is scientifically important for understanding hydration processes in silicates and low-temperature metamorphism.
🌍 Origins and Naming
- First Described: 1925
- Name Origin: Named after Alpheus Fuller Williams (1874–1953), General Manager of De Beers Consolidated Mines in Kimberley, South Africa.
- Type Locality: Dutoitspan diamond mine, Kimberley, and Wessels mine near Kuruman, Cape Province, South Africa.
🔬 Chemical and Structural Properties
- Formula: Ca₃(SiO₃OH)₂·2H₂O
- Mineral Group: Nesosilicates
- Crystal System: Monoclinic
- Color: Colorless to white
- Habit: Prismatic, tabular, radial fibrous, or massive crystals
- Hardness: 3–4 on Mohs scale
- Specific Gravity: ~2.63
- Luster: Vitreous
- Streak: White
- Optical Properties: Biaxial (+), refractive indices nα = 1.617, nβ = 1.620, nγ = 1.634
- Other: Piezoelectric properties have been observed.
⚙️ Geological Occurrence
Afwillite forms in:
- Contact metamorphism of limestones (skarn environments)
- Hydrothermal settings where calcium-rich fluids interact with silicates
- Cement chemistry: It can appear in hydrated Portland cement phases, making it relevant to construction material science
📍 Notable Localities
- South Africa: Kimberley diamond mines (type locality)
- California, USA: Crestmore Quarry, Riverside County
- Other skarn deposits worldwide where calcium silicate hydrates occur.
📖 Scientific and Collector Significance
- Petrology: Important for understanding low- to moderate-temperature silicate hydration and stability.
- Materials Science: Studied in relation to cement hydration and degradation processes, linking mineralogy with engineering applications.
- Collectors: Rare and delicate crystals, not common in large specimens, but valued for their unusual fibrous or bladed habits.
✨ Conclusion
Afwillite is a calcium hydroxide nesosilicate mineral with a distinctive role in both geology and materials science. Though rare and not a mainstream collector’s mineral, it is scientifically significant for its occurrence in metamorphosed limestones and its relevance to cement chemistry.
In short: Afwillite is a rare calcium silicate hydrate mineral, first described in South Africa, important in both geology and cement science.
