A clinopyroxene (monoclinic, C2/c space group) with a chemical composition of (Mg,Fe,Ca)(Mg,Fe)Si₂O₆ where Ca is between about 5 to 15 mole % of CaSiO₃ (wollastonite component). Pigeonite forms where the basaltic melt is relatively quickly cooled in, for example, minor shallow intrusions.

A clay mineral intercalated with small organic or inorganic complexes (or “pillars”), which do not completely fill the interlayer space. The size and shape of the resultant cavities (or “galleries”) are determined by the size, shape, and orientation of the pillars. Pillared clays are potentially useful to remove organic molecules based on shape-selective adsorption (“molecular sieves”). For clays, intercalations involve positively charged complexes (either organic or inorganic “cations”) to offset the negatively charged layers of the clay. Common types of complexes include those of the methylammonium group (organic) and the Keggin ion (Al13, inorganic). Other types of layered materials can also be pillared.
See Keggin ion.
Cf., zeolite

A kerolite-like phase where Ni > Mg.

Not a valid mineral species, but is often used to describe Ni-rich, 2:1 layer silicates with additional structural H₂O.
Cf., kerolite

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.

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).