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Attapulgite

Palygorskite
Mineraly.sk - palygorskit.jpg
A sample of palygorskite
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

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