Gypsum vs Talc
| Property | Gypsum | Talc |
|---|---|---|
| Formula | CaSO4 · 2H2O | Mg3Si4O10(OH)2 |
| Crystal System | Monoclinic | Monoclinic |
| Mineral Class | 07 Sulfates, Chromates, Molybdates, and Tungstates | 09 Silicates |
| Mohs Hardness | 1.5-2.0 | 1.0 |
| Color | Colorless, white, gray, yellow, brown | White, gray, green, pale blue |
| Luster | Vitreous | Pearly |
| Streak | White | White |
| Transparency | Transparent | Translucent |
| Cleavage | Perfect {010} | Perfect {001} |
| Fracture | Conchoidal | Uneven |
Key Differences
- ◆ Talc (hardness 1) is the softest mineral; gypsum (hardness 1.5–2) is slightly harder.
- ◆ Talc has a distinctive soapy feel; gypsum does not.
- ◆ Talc is a magnesium silicate Mg3Si4O10(OH)2; gypsum is a hydrated calcium sulfate CaSO4·2H2O.
- ◆ Gypsum is used extensively in plaster and drywall; talc is used in cosmetics and ceramics.
- ◆ Talc has pearly luster; gypsum can be vitreous, silky (satin spar), or massive (alabaster).