dickite

Dickite is a clay mineral in the kaolinite group. It is a hydrous aluminum silicate with the broad formula Al2Si2O5(OH)4 and is considered a kaolinite polytype that forms as well-crystallized, plate-like crystals or microcrystalline masses. Dickite differs from the common kaolinite by having a higher degree of structural order and crystallinity, which leads to distinct and sharper X-ray diffraction patterns.

As a 1:1 phyllosilicate, dickite consists of alternating tetrahedral silica sheets and octahedral aluminum hydroxide sheets. The more ordered stacking of these layers distinguishes it from other kaolinite polytypes such as nacrite and halloysite. Dickite is typically described as forming under relatively low-temperature hydrothermal conditions or during diagenetic alteration of aluminous rocks, and it can be found in some sedimentary rocks and hydrothermal veins.

Occurrence and associations: dickite has been reported in a variety of localities worldwide, often in environments where feldspars and other aluminous minerals are chemically altered. It commonly occurs with minerals such as quartz and other clay minerals, and its presence can indicate specific alteration histories.

Physical properties: dickite is usually white to cream in color, with an earthy to pearly luster. It has a soft feel, with a Mohs hardness around 2–2.5, and shows perfect basal cleavage typical of kaolinite group minerals. Its well-ordered structure can influence its texture and appearance relative to more disordered kaolinite.

Dickite serves as a reference mineral in clay mineralogy for differentiating kaolinite polytypes and in X-ray diffraction analyses of layered silicates.