An obsolete name for altered material, probably vermiculite.

A modulated 1:1 layer silicate with a continuous, planar octahedral sheet and a general chemical composition of M²⁺₈T₆O₁₅(OH,Cl)₁₀. Pyrosmalite is the M = Mn, Fe series, manganpyrosmalite is M for Mn > Fe, and ferropyrosmalite is M for Fe > Mn. Friedelite is the Mn end member and a disordered (polytypic) equivalent of mcGillite. In addition, mcGillite has several additional polytypes. The pyrosmalite structure has an equal number of tetrahedra coordinating to two adjacent octahedra sheets via tetrahedral apical oxygen atoms (Kato and Takéuchi, 1983). Each tetrahedral sheet is composed of 4-, 6-, and 12-fold tetrahedral rings linked laterally, with half of the tetrahedra in the 4- and 12-fold rings inverted. Schallerite and nelenite are polymorphs and similar to friedelite, but apparently with As₃O₆ molecules within the 12-fold rings. Arsenite analogues of pyrosmalite-type minerals (T = As) occur: manganarsite (analogue manganpyrosmalite), and unnamed arsenite equivalents of schallerite and friedelite. Phase assemblages and occurrences are complex. Pyrosmalite occurs in greenschist facies manganiferous rocks. A near Fe-rich end member was reported from low-grade Fe- and Mn-rich sulfide deposits near Mt. Isa, Queensland, Australia. Friedelite occurs in low-grade metamorphic rocks and is Cl bearing.

The pyroxene group minerals are single-chain silicates with repeat units of two SiO₄ tetrahedra (~ 5.2Å) along the chain direction (c-axis). Chemical formulae, using site nomenclature, are given by: M2M1T₂O₆, where M2 represents medium- to large-size cations, commonly Ca²⁺, Na⁺, Fe²⁺, Mg²⁺, Mn²⁺, and Li⁺; M1 represents small- to medium-size cations like Fe²⁺, Mg²⁺, Al³⁺, Fe³⁺, and Ti⁴⁺; and T represents Si⁴⁺ and Al³⁺ in tetrahedral sites. The minerals develop good {110} cleavage, with cleavage angles near 90 degrees. The pyroxene group is divided further to subgroups according to composition (and symmetry). The common pyroxenes form solid solutions of the Ca-Mg-Fe pyroxenes and are compositionally described (e.g., Morimoto et al., 1988) in the pyroxene quadrilateral with end-members diopside (Di: CaMgSi₂O₆), hedenbergite (Hd: CaFeSi₂O₆), enstatite (En: Mg₂Si₂O₆), and ferrosilite (Fs: Fe₂Si₂O₆). The enstatite-ferrosilite solid solution series forms orthopyroxenes (OPX) with orthorhombic (Pbca) symmetry, whereas, the diopside-hedenbergite solid solution series forms clinopyroxenes (CPX) with monoclinic (C2/c) symmetry. Weathering reactions of pyroxene group minerals often produce clay minerals. Pyroxene end-members are: enstatite Mg₂Si₂O₆ (polymorphs clinoenstatite, orthoenstatite, protoenstatite); ferrosilite Fe₂Si₂O₆; diopside CaMgSi₂O₆; hedenbergite CaFeSi₂O₆; jadeite NaAlSi₂O₆; aegirine NaFeSi₂O₆; spodumene LiAlSi₂O₆; pigeonite (Mg,Fe,Ca)(Mg,Fe)Si₂O₆; augite (Ca,Mg,Fe²⁺,Fe³⁺,Ti,Al)₂(Si,Al)₂O₆; omphacite (Ca,Na)(Mg,Al)Si₂O₆; grossmanite CaTiSiAlO₆. Refer to individual end members for further descriptions.

single-chain silicate minerals with Si-tetrahedral repeats of 3 (e.g., in wollastonite, CaSiO3), 5 (e.g., in rhodonite, MnSiO3), 7 (e.g., in pyroxmangite, FeSiO3), or 9 (e.g., in ferrosilite III). In contrast, the pyroxene tetrahedral repeat is 2. However, both the pyroxenoids and the pyroxenes have octahedrally coordinated cations connecting to the tetrahedral chains in similar ways. Hydrous pyroxenoids exist also, where Na + H substitute for one of the divalent cations, e.g., pectolite, Ca2NaH(SiO3)3. Wollastonite occurs as a contact metamorphic mineral of siliceous dolomites and is used in the manufacture of tile and in glazes. Rhodonite and pyroxmangite occur in manganese deposits and metamorphosed Mn-rich iron formations. Pectolite, commonly associated with zeolites, forms in cavities in basalts as a secondary mineral formed by hydrothermal activity.

Single-chain silicate minerals with Si-tetrahedral repeats of 3 (e.g., in wollastonite, CaSiO₃), 5 (e.g., in rhodonite, MnSiO₃), 7 (e.g., in pyroxmangite, FeSiO₃), or 9 (e.g., in ferrosilite III). In contrast, the pyroxene tetrahedral repeat is 2. However, both the pyroxenoids and the pyroxenes have octahedrally coordinated cations connecting to the tetrahedral chains in similar ways. Hydrous pyroxenoids exist also, where Na + H substitute for one of the divalent cations, e.g., pectolite, Ca₂NaH(SiO₃)₃. Wollastonite occurs as a contact metamorphic mineral of siliceous dolomites and is used in the manufacture of tile and in glazes. Rhodonite and pyroxmangite occur in manganese deposits and metamorphosed Mn-rich iron formations. Pectolite, commonly associated with zeolites, forms in cavities in basalts as a secondary mineral formed by hydrothermal activity.

See pyroxenoid group.

A calculation of atomic or molecular properties of a model system based on first principles (ab initio) quantum mechanics. Because quantum calculations involve either the solution or approximation of the Schrodinger equation to determine the electronic structure, this is the highest level of theory that can be used to calculate molecular-scale properties of a model system.
Cf., density functional theory

Quartz, SiO2, is comprised of two chains, both spirals of SiO4 tetrahedra parallel to the c axis. In the alpha-quartz structure (low temperature form to 573 oC at 1 bar), these chains are kinked and the structure has trigonal symmetry. In the beta-quartz structure (high temperature form, above 574.3 oC), the chains expand (the tetrahedra are not twisted) and the symmetry is hexagonal with a more open structure than the alpha form. The beta form is non-quenchable and not found under ambient conditions. An intermediate phase between 573 – 574.3 oC is known to exist. Quartz is a common associated phase in clay, but generally forms grains larger than clay particles (about 0.2 – 0.4 micrometers) and therefore quartz particles can be removed by size separation.

Quartz, SiO₂, is comprised of two chains, both spirals of SiO₄ tetrahedra parallel to the c axis. In the alpha-quartz structure (low temperature form to 573 ^oC at 1 bar), these chains are kinked and the structure has trigonal symmetry. In the beta-quartz structure (high temperature form, above 574.3 ^oC), the chains expand (the tetrahedra are not twisted) and the symmetry is hexagonal with a more open structure than the alpha form. The beta form is non-quenchable and not found under ambient conditions. An intermediate phase between 573 – 574.3 ^oC is known to exist. Quartz is a common associated phase in clay, but generally forms grains larger than clay particles (about 0.2 – 0.4 micrometers) and therefore quartz particles can be removed by size separation.

Quartzine is a rock term to describe a mixture of a fibrous [0001] variety of microcrystalline (length slow) quartz and moganite. Cf., chalcedony