Sands & Clays
Andalusite
Andalusite is one of the three crystalline forms of aluminium silicate (Al₂SiO₅) in the sillimanite group and a premium raw material for high-alumina refractories. On heating it converts gradually — without sudden decomposition — into mullite and a glassy phase, and this controlled mullitisation with minimal volume expansion delivers excellent thermal-shock resistance, creep resistance and dimensional stability at high temperature.
Typical Analysis
| Composition | Mean (%) | Range of five samples |
|---|---|---|
| Al₂O₃ | 58.52 | 57.36 - 59.05 |
| SiO₂ | 39.31 | 38.82 - 40.25 |
| Fe₂O₃ | 0.55 | 0.53 - 0.61 |
| K₂O | 0.39 | 0.36 - 0.44 |
| Na₂O | 0.13 | 0.09 - 0.16 |
| TiO₂ | 0.12 | 0.11 - 0.15 |
| MgO | 0.11 | 0.10 - 0.13 |
| CaO | 0.09 | 0.06 - 0.12 |
| L.O.I | 0.73 | 0.60 - 0.91 |
| P₂O₅ · MnO | < 0.01 | Below detection limit |
| S | < 0.02 | Below detection limit |
Key Properties
| Formula | Al₂SiO₅ (sillimanite group) |
|---|---|
| Typical alumina | 58.5 % |
| Iron | 0.55% — below typical commercial andalusite |
| Total alkalis | ≈ 0.5% (Na₂O + K₂O) |
| Thermal behaviour | Gradual mullitisation, low expansion |
| Key characteristic | High creep and thermal-shock resistance |
