Palygorskite
| Palygorskite | |
|---|---|
A sample of palygorskite
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| General | |
| Category | Phyllosilicate |
|
Formula (repeating unit) |
(Mg,Al)2Si4O10(OH)·4(H2O) |
| Strunz classification | 9.EE.20 |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | C2/m |
| 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 | Lath shaped crystals, fibrous and compact masses |
| Cleavage | Distinct/good, good on {110} |
| Tenacity | Tough |
| Mohs scale hardness | 2 - 2.5 |
| Luster | Waxy, earthy |
| Diaphaneity | Translucent |
| Specific gravity | 1 - 2.6 |
| 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 |
| References | |
Palygorskite or attapulgite is a magnesium aluminium phyllosilicate with 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.
Palygorskite was first described in 1862 for a deposit at Palygorskaya on the Popovka River, Middle Urals, Permskaya Oblast, Russia.
The synonym attapulgite is derived from the U.S. town of Attapulgus, in the extreme southwest corner of Georgia, where the mineral is abundant and surface-mined.
Two companies are involved in the industrial extraction and processing of gellant-grade attapulgite clay within the same Attapulgus deposit: Active Minerals International, LLC, and BASF Corp. In 2008, BASF acquired the assets of Zemex Attapulgite, leaving only two gellant-grade producers. Active Minerals operates a dedicated factory to produce the patented product Actigel 208 and built a new state-of-the-art production process in early 2009 involving portable plant processing at the mine site.
Attapulgite clays are a composite of smectite and palygorskite. Smectites are expanding lattice clays, of which bentonite is a commonly known generic name for smectite clays. The palygorskite component is an acicular bristle-like crystalline form that does not swell or expand. Attapulgite forms gel structures in fresh and salt water by establishing a lattice structure of particles connected through hydrogen bonds.
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Wikipedia