Hydrotalcite
| Hydrotalcite | |
|---|---|
| General | |
| Category | Carbonate mineral |
| Formula | Mg6Al2CO3(OH)16·4H2O |
| IMA symbol | Htc |
| Strunz classification | 5.DA.50 |
| Crystal system | 3R polytype: Trigonal 2H polytype: Hexagonal |
| Crystal class | 3R polytype: Hexagonal scalenohedral (3m) H-M symbol: (3 2/m) 2H polytype: Dihexagonal dipyramidal (6/mmm) |
| Space group | R3m |
| Unit cell | a = 3.065 Å, c = 23.07 Å; Z = 3 |
| Identification | |
| Color | White with possible brownish tint |
| Crystal habit | Subhedral platey crystals, lamellar-fibrous, rarely euhedral prismatic; commonly foliated, massive |
| Cleavage | {0001}, perfect |
| Tenacity | Flexible, not elastic |
| Mohs scale hardness | 2 |
| Luster | Satiny to greasy or waxy |
| Streak | White |
| Diaphaneity | Transparent |
| Specific gravity | 2.03–2.09 |
| Optical properties | Uniaxial (−) |
| Refractive index | nω = 1.511 – 1.531 nε = 1.495 – 1.529 |
| Birefringence | δ = 0.016 |
| Other characteristics | Greasy feel |
| References | |
Hydrotalcite, or formerly also völknerite, is a layered double hydroxide (LDH) of general formula Mg6Al2CO3(OH)16·4H2O, whose name is derived from its resemblance with talc and its high water content. Multiple structures containing loosely bound carbonate (CO2−3) ions exist. The easily exchangeable carbonates enable applications of the mineral in wastewater treatment and the immobilisation of radioactive waste after nuclear fuel reprocessing.