See rotation symmetry.

A high-temperature, orthorhombic (Pbcn) polymorph of enstatite. Protoenstatite has been thought to be unquenchable, and commonly transforms to clinoenstatite at low temperature in experiments. However, natural nanoparticle-size protoenstatite has been reported in gem quality “watermelon” sunstones from Oregon, U.S.A. and are apparently quenchable from high-temperature and high-pressure conditions as nanoparticles (Xu et al., 2017).

An obsolete varietal term for zinnwaldite, lithian annite, and lithian siderophyllite.

An obsolete name for opal.
See opal

An obsolete name for opal or quartzine.

A poorly defined material, possibly interstratified biotite and vermiculite or interlayer-deficient biotite.

See microfabric, clay.

A pseudomorph is an alteration product of a crystal that preserves the external euhedral crystal form of the precursor mineral. The pseudomorph may have a different chemical composition and/or crystal structure than the precursor crystal. The pseudomorph can result from replacement of the original structural bonds by formation of new bonds that minimize the energy toward equilibrium in response to changes in the chemical (T, P, X) environment.
Cf., alteromorph, centripetal replacement

An obsolete term for a compact, massive chlorite that resembles serpentine.

An obsolete term for poorly defined material, impure halloysite.