See astrophyllite group.

Weight loss after heating, and (usually) subsequent cooling, to determine the presence of volatiles in a solid.
Cf., water, structural; water, adsorbed

A member of the palygorskite-sepiolite group with a composition of approximately Na₄Mg₆ (Si₁₂O₃₀)(OH)₄ (OH₂)₄.
See palygorskite-sepiolite group

An industrial term referring to superheated but not fully calcined clays.
Cf., superheating

In geotechnical engineering, low-activity clays have activities of < 1, and include illite, chlorite, and kaolinite. Fe and Al oxide minerals and clay-sized primary minerals are also considered low activity. See activity, clay; high-activity clays; quick clays

A poorly described material originally thought to be a “swelling” talc in old literature, but probably saponite, and now considered as an obsolete term.

a) Industrial/clay: A lumen is the bore of a tube. Thus, halloysite is a tubular mineral with an approximately 30 nanometer diameter lumen that runs the length of the tube.

b) Medical: A cavity of passage in a tubular organ; e.g., the lumen of the intestine. Also, commonly applied to those clay minerals where medications are loaded into the tube bore, and the clay particle is coated with an excipient to control the timing of delivery.

Luogufengite is an Al-bearing iron oxide (epsilon-Fe₂O₃) polymorph that occurs as a nanomineral with large magnetic coercivity (resistant to be affected by an external magnetic field). The structure is orthorhombic with doubled hexagonal (i.e., ABAC) packing of oxygen atoms. Luogufengite occurs as an oxidation product of Fe-bearing basaltic lava or glass at high temperature, and is associated with maghemite and hematite (Xu et al., 2017). The mineral transforms into hematite (alpha-Fe₂O₃) when the crystal size reaches ~100 nm or larger (Lee and Xu, 2016). Luogufengite may affect high-remnant magnetization of some igneous and metamorphic rocks.

See opal.

Appearance of a mineral surface in reflected light.