An obsolete term for nontronite.

A poorly defined material, possibly a pseudomorph mostly of mica after cordierite, nepheline, or scapolite.

An obsolete term for saponite.

See plane light.

Plagioclase feldspar minerals occur in the solid solution series between albite [Ab: Na(Si₃Al)O₈] and anorthite [An: Ca(Si₂Al₂)O₈] end-members. Ordering between Al and Si is very sluggish in the plagioclase feldspars and requires a coupled substitution between (Si + Na) and (Al + Ca). The plagioclase feldspar minerals are the most abundant minerals in the earth’s crust. Plagioclase mineral names are divided into albite (An_0-10), oligoclase (An_10-30), andesine (An_30-50), labradorite (An_50-70), bytownite (An_70-90), and anorthite (An_90-100), but it is increasingly common to designate molecular percentages (i.e., Or₁₀Ab₆₀An₃₀, where Or = orthoclase and Ab and An are defined above). Labradorite feldspar may show iridescent colors at compositions of An₅₀–₆₀ and with Or₂–₅ where semi-periodic exsolution lamellae occur with periodicity of ~100 nm to ~300 nm. Labrodorite commonly occurs in gabbroic rocks or anorthosites (plagioclase-dominated rocks) that experienced extremely slow cooling history. Plagioclase feldspars are used in glass making and ceramics, paints, rubber, and plastics, although the alkali feldspars are more commonly used in industry.
Cf., alkali feldspar

In phyllosilicate mineralogy, a set of one or more types of atoms (e.g., a plane of Si and Al atoms, a plane of basal oxygen atoms) that form a two-dimensional flat or nearly flat surface.
See Guggenheim et al. (2006) and references therein.
Cf., sheet, layer

Polarized light, or plane light, is light that vibrates within a single plane (“plane of vibration”) which is defined as the plane parallel to the ray’s path and its vibration direction. The polarized light results from the introduction of a single polarizing device into the optic path of a petrographic (polarized light) microscope, with the plane of vibration obtained from the privileged direction of the polarizer.
See petrographic microscope. Abbr. PL, or PPL (plane polarized light).

See plane light.

See plane light.

See soil plasma.