Aliettite
Chemical formula: Ca<sub>0.2</sub>Mg<sub>6</sub>(Si,Al)<sub>8</sub>O<sub>20</sub>(OH)<sub>4</sub>·4H<sub>2</sub>O
Aliettite is a rare clay mineral, a regular interstratification of talc and saponite, occurring as soft, platy aggregates.
Description
## Characteristics Aliettite is a rare mineral from the layered silicate (phyllosilicate) group, classified as a clay mineral. Structurally, it is an ordered 1:1 interstratification of talc and saponite. For this reason, it is not recognized by the IMA as a distinct mineral species but rather as a specific, regular mixed-layer structure. It occurs as very soft, fine-grained, and plastic aggregates with a platy or foliated habit. Individual lamellae are flexible but inelastic. ## Physical Properties It is characterized by exceptionally low hardness, only 1 on the Mohs scale, meaning it can be scratched with a fingernail. Its luster is most often pearly on cleavage surfaces, and can also be waxy or dull in compact aggregates. It is translucent to opaque. The mineral's density is approximately 2.5-2.6 g/cm³. ## Colors and Varieties Aliettite is typically white, yellowish-white, or pale green. It does not form color varieties or commercial forms; its name refers strictly to a defined mineralogical structure. ## History and Name The mineral was described in 1969 by Franco Veniale and named after Andrea Alietti (1923–2000), a professor of mineralogy at the University of Modena in Italy, for his contributions to the study of clay minerals. The type locality is Monte Chiaro in the Taro River valley (Parma Province, Italy). ## Uses Aliettite has no industrial applications. It is solely an object of scientific interest and is sought after by specialized collectors of rare and systematic minerals.
Diagnostic features
## Identification Key diagnostic features of aliettite include its extreme softness (hardness 1 on the Mohs scale), pearly luster on cleavage planes, and characteristic flexible lamellae. To the touch, it may feel slightly greasy or soapy. Its occurrence in veins cutting serpentinites is a strong indicator. Final and certain identification is almost exclusively possible using X-ray diffraction (XRD), which allows distinguishing its regular interstratified structure from ordinary talc or saponite. ## Differentiation from Similar Minerals Aliettite is macroscopically almost impossible to distinguish from talc, with which it is structurally related and often co-occurs. Talc has very similar physical properties. It can also be confused with other clay minerals, such as saponite or pyrophyllite. Saponite is characterized by its ability to swell in water, which aliettite does not exhibit to the same extent. Pyrophyllite occurs in different geological environments (aluminum-rich rocks). ## Crystal Forms Aliettite does not form well-developed, macroscopic crystals. It occurs as fine-grained, scaly, platy, or foliated aggregates. Sometimes it forms fibrous or radial veins within the host rock.
Geological environment
## Genesis Aliettite is a product of low-temperature hydrothermal processes. It forms through the alteration of ultramafic rocks, primarily serpentinites. It develops in veins and fractures, often as an alteration product of magnesium minerals. ## Mineral Associations This mineral most commonly co-occurs with talc, saponite, minerals from the serpentine group (such as antigorite and chrysotile), chlorite, calcite, and dolomite. ## Localities The most important and classic localities for aliettite are in Italy, particularly at the type locality of Monte Chiaro (Taro valley, Parma) and in Val di Susa (Piedmont). These are the main sources of well-identified specimens of this mineral.
Rarity
Rare
Collector aspects
## Quality Criteria As a rare and visually unattractive mineral for the typical collector, aliettite is valued primarily in systematic collections. The value of a specimen is determined primarily by the purity of the material, its quantity, and accurate identification confirmed by analysis. Well-documented provenance, especially if it is a type locality, enhances its appeal. It does not form aesthetic crystals, so criteria such as form or transparency are not applicable. ## Popular Localities The most prized specimens by specialized collectors are those from Italian localities, especially from Monte Chiaro in the province of Parma, where the first described samples originated.
Care and storage
## Cleaning The mineral is extremely soft and sensitive to water. It should not be washed in water or other liquids, as it can absorb moisture, swell, or disintegrate. For dust removal, a very soft, dry brush can be used with extreme care. ## What to Avoid Contact with water, chemicals, acids, and detergents should be strictly avoided. The mineral is sensitive to pressure and easily scratched or permanently deformed. It should be protected from high temperatures and sudden changes in humidity. ## Storage Aliettite specimens are best stored in closed, padded "perky boxes" to protect them from mechanical damage, dust, and humidity fluctuations. It should not be displayed on open shelves.