Palygorskite

Chemical formula: (Mg,Al)₂Si₄O₁₀(OH)·₄H₂O

Palygorskite is a hydrated magnesium aluminum silicate, forming characteristic, light, and porous aggregates with a skin-like or paper-like structure.

## Characteristics Palygorskite, also known as attapulgite, is a clay mineral belonging to the layered silicate group. Its unique crystalline structure, consisting of alternating ribbons and channels, gives it exceptional properties such as a large specific surface area and high porosity. Typical specimens appear as compact, skin-like or paper-like masses, which feel light and somewhat greasy to the touch. It rarely forms visible crystals, most often occurring as fibrous, felted, or earthy aggregates. Due to its ability to absorb water, it becomes plastic when wet. ## Physical Properties This mineral is very soft, with a Mohs hardness of 2 to 2.5. It is exceptionally light, with a density of approximately 2.15 g/cm³, and some dry, porous aggregates can even float on water, hence its former name "sea foam". The luster is usually dull, earthy, or waxy. It is opaque or translucent in thin fragments. ## Colors and Varieties It most commonly occurs in shades of white, gray, yellow, brown, or greenish. The color depends on chemical impurities, mainly iron compounds. The name attapulgite is a synonym for palygorskite and comes from the location in Attapulgus, Georgia (USA), where large deposits are found. Other historical names, such as "mountain leather" or "mountain cork," refer to its specific physical forms. ## History and Name The name palygorskite comes from its discovery site in the Palygorskaya mine in the Urals, Russia. The mineral was first described by T.V. Savchenkov in 1862. The name attapulgite was introduced by the French mineralogist Jean-Pierre

Properties

Mohs hardness: 2-2.5
Color: White. grayish, yellowish, gray-green
Luster: Dull
Streak: White
Density: 2.1
Cleavage: Good on {110}
Fracture: Uneven
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Palygorskite is most easily identified by its unique physical properties. It is very light, often porous, and soft (it can be scratched with a fingernail). Its felted, skin-like, or paper-like aggregates are characteristic. When wet, it becomes plastic and can stick to the tongue. These features distinguish it from most other minerals. ## Distinguishing from Similar Minerals It can be confused with other clay minerals, such as sepiolite or kaolinite. Sepiolite has very similar properties and uses, and a definitive distinction often requires X-ray diffraction (XRD) analysis. Kaolinite is also soft and earthy but usually does not form fibrous or skin-like aggregates and is not as light as palygorskite. Chrysotile (serpentine asbestos) forms fibrous aggregates but is more silky and elastic. ## Crystal Forms Well-formed crystals are extremely rare. Palygorskite mainly forms microscopic, acicular or lath-like crystals that combine into massive aggregates. These aggregates take fibrous, felted, earthy forms, as well as characteristic structures referred to as "mountain leather," "mountain cork," or "mountain paper."

Geological environment

## Genesis Palygorskite is a secondary mineral, formed by the weathering of magnesium-rich rocks, such as serpentinites, pyroxenites, or dolomites, under arid or semi-arid climatic conditions. It forms in soils, lacustrine, and marine sediments, often in alkaline and saline environments. It can also form through low-temperature hydrothermal processes, filling fissures and fractures in various rock types. ## Mineral Associations It co-occurs with other clay minerals, such as montmorillonite, sepiolite, and illite. It is also often accompanied by calcite, dolomite, quartz (in the form of chalcedony or opal), and minerals from the zeolite group. ## Localities Significant industrial deposits are found in the United States (Attapulgus in Georgia and Quincy in Florida). Other important localities include Spain (Madrid region), Senegal, Saudi Arabia, China, Ukraine, and Russia (Urals). In Poland, occurrences have been noted in the vicinity of Ząbkowice Śląskie in Lower Silesia.

Rarity

Not very common

For collectors

## Quality Criteria Palygorskite is rarely sought after by collectors for its aesthetic qualities, as it usually forms inconspicuous, earthy, or compact masses. However, specimens with well-formed, unusual shapes, such as "mountain leather" or "mountain paper," are exceptionally valued, especially if they are large and well-preserved. Purity and uniform color (most often white) can enhance the specimen's attractiveness. Due to its fragility, undamaged specimens are more valuable. ## Popular Localities For collectors seeking unusual forms, specimens from historical localities in Russia (Urals) or classic sites in the USA (Georgia, Florida) may be of interest. Specimens from these locations have historical significance and are representative of this mineral.

Care and storage

de Lapparent in 1935. ## Uses Palygorskite has numerous industrial applications due to its high absorption capacity, high-temperature resistance, and chemical inertness. It is used as an absorbent in cat litter, as a filtering and decolorizing agent for oils and waxes, and as a filler in paints, plastics, and rubber. In pharmacy and cosmetics, it serves as a thickener and stabilizer in suspensions. In agriculture, it improves soil structure and water retention.