Corundum vs Spinel
| Property | Corundum | Spinel |
|---|---|---|
| สูตรเคมี | Al2O3 | MgAl2O4 |
| ระบบผลึก | Trigonal | Cubic (Isometric) |
| หมวดหมู่แร่ธาตุ | 04 Oxides and Hydroxides | 04 Oxides and Hydroxides |
| ความแข็งโมห์ส | 9.0 | 7.5-8.0 |
| สี | Red (ruby), blue (sapphire), various colors | Red, blue, green, black, colorless |
| ความวาว | Adamantine | Vitreous |
| สีเส้นขูด | Colorless | White |
| ความโปร่งใส | Transparent | Transparent |
| การแตกเรียบ | None | None |
| รอยแตก | Conchoidal to uneven | Conchoidal |
Key Differences
- ◆ Corundum (hardness 9) is harder than spinel (hardness 7.5–8); corundum is the second hardest natural mineral.
- ◆ Both produce red gemstones — ruby (corundum) and red spinel — that were historically confused for centuries.
- ◆ Corundum is a trigonal oxide (Al2O3); spinel is a cubic oxide (MgAl2O4).
- ◆ Corundum has no cleavage; spinel also has no cleavage — both show conchoidal fracture.
- ◆ Spinel occurs in metamorphosed limestones; corundum forms in a wider range of igneous and metamorphic rocks.