a) Petrologic term: rock composed primarily of kaolinite, nacrite, dickite, or halloysite (i.e., minerals of the kaolin group). In most case, the identification of the specific species is unknown. The rock is commonly white, earthy, and soft.

b) Mineralogic term: a sub-group name (within the group “serpentine-kaolin”) for those phyllosilicates that are dioctahedral, with 1:1 layers, and with a net layer charge of approximately 0.0. Species of this sub-group include kaolinite, nacrite, dickite and halloysite. Previously, the group name was “serpentine-kaolinite”, and the subgroup name was “kaolinite”, but this scheme created confusion because it was unclear if “kaolinite” was referring to the more general sub-group or the species “kaolinite”.
See also Part 2 of the Glossary.
Cf., dioctahedral, 1:1 layers

A white to gray clayey-textured rock predominantly composed of kaolin group minerals (primarily kaolinite). Hard kaolin is fine grained, difficult to break, and commonly with sharp, protruding (jagged) edges. Hard kaolin requires more complex mine extraction and mineral processing techniques than “soft kaolin” (kaolin-rich rock that is smooth to the touch, weak, and friable).

See kaolin, hard.

A member of the kaolin group (1:1 layer, dioctahedral), and polymorphic with dickite and nacrite. The chemical composition is Al₂Si₂O₅(OH)₄. In kaolinite, the vacant octahedral site is located in the “B” site in each layer to form a triclinic structure. The “B” and “C” sites would be related by a mirror plane if both sites were occupied identically within the same layer, whereas the “A” site resides on the mirror plane (Bish and Von Dreele, 1989). Kaolinite forms under diagenetic and hydrothermal conditions, and may transform to dickite at higher temperatures. At very high temperatures, kaolinite transforms to “metakaolinite”. In early publications, kaolinite was used as the group name, now known as kaolin.
Cf., dickite, halloysite, kaolin, nacrite

Superceded by kaolin subgroup.

Superceded by kaolin-serpentine group.

A non-regular interstratification of kaolinite-like layers with smectite-like layers. Alternatively, the smectite-like layer may be replaced with other expandable layers (e.g., vermiculite). Found in paleosols. May be abbreviated K/S or K-S, and has been referred to as an “kaolinite/expandable” interstratification, K/E (Hughes et al., 1993).

A commercial product (made by Chattem, Inc.) involving a formulation of kaolin and pectin that was used as an anti-diarrheal. Since 2003, the formulation was changed to bismuth subsalicylate, but some formulations containing attapulgite as the active principle are sold in Canada.

An aluminum-rich Keggin-type structure is commonly used as a pillaring agent in clays. This complex has a composition of Al₁₃O₄(OH)₂₄(H₂O)₁₂)⁷⁺, and is often referred to as Al₁₃. Other compositions with the Keggin structure are possible, but they have not been as extensively studied in pillared clays. Keggin structures are of commercial interest because they are catalysts.
See pillared clay.

A platy serpentine mineral of ideal composition of Mn₂Al(Si,Al)O₅(OH)₄, and thus, the Mn²⁺ analogue of amesite. Mg and Fe²⁺ have been found to substitute for Mn and Al. Natural occurrences are rare; the type locality is Bald Knob, North Caroline, USA. Stacking disorder is common but, two-layer (2H₂) and six-layer polytypes are known to occur.
Cf., amesite, zinalsite