Palygorskite
| Palygorskite | |
|---|---|
| General | |
| Category | Phyllosilicate |
| Formula | (Mg,Al)2Si4O10(OH)·4(H2O) Al2Mg2◻2Si8O20(OH)2(H2O)4 · 4H2O |
| IMA symbol | Plg |
| Strunz classification | 9.EE.20 |
| Crystal system | Monoclinic, orthorhombic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | B2/m and setting C2/m, P 21 21 21 |
| Unit cell | a = 12.78 Å, b = 17.86 Å, c = 5.24 Å; β = 95.78°; Z = 4 |
| Identification | |
| Color | White, grayish, yellowish, gray-green |
| Crystal habit | Commonly fibrous, tangled mats known as mountain leather. Individual, small crystals are lath-shaped |
| Cleavage | Distinct/good, good on {110} |
| Tenacity | Tough |
| Mohs scale hardness | 2 – 2.5 |
| Luster | Waxy, earthy |
| Diaphaneity | Translucent |
| Specific gravity | 1 – 2.6 |
| Density | 2.1 - 2.6 g/cm3 (Measured); 2.35 g/cm3 (Calculated) |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.522 – 1.528 nβ = 1.530 – 1.546 nγ = 1.533 – 1.548 |
| Birefringence | δ = 0.011 – 0.020 |
| Pleochroism | X= pale yellow Y=Z= pale yellow-green |
| Common impurities | Fe,K |
| References | |
Palygorskite (Russian: Палыгорскит) or attapulgite is a magnesium aluminium phyllosilicate with the chemical formula (Mg,Al)2Si4O10(OH)·4(H2O) that occurs in a type of clay soil common to the Southeastern United States. It is one of the types of fuller's earth. Some smaller deposits of this mineral can be found in Mexico, where its use is tied to the manufacture of Maya blue in pre-Columbian times.