An obsolete term for paragonite.

A trioctahedral member of the true mica group. The end-member formula is NaMg₂Al(Al₂Si₂)O₁₀(OH)₂. The first occurrence of preiswerkite is from a metamorphosed basic dike in the Geisspfad ultramafic complex in the Penninic Alps. The 1M, 2M₁ and 1M_d polytypes have been identified.
Cf., aspidolite, eastonite

See hollandite.

Primary mineral is a mineral of igneous, metamorphic or sedimentary origin now residing in weathering, sedimentary, diagenetic or hydrothermal environments where many alteration processes operate. A primary mineral is present in the parent rock; thus, in soils and other weathering or alteration environments, a primary mineral is one that remains from the parent rock whereas a secondary mineral is one that forms as the rock weathers.
Cf., secondary mineral

A crystal shape where one dimension is considerably greater than the other two.

A discredited name for an often iron-rich, but Si-poor chlorite.

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.