pigeonite


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pigeonite

[′pij·ə‚nīt]
(mineralogy)
(Mg,Fe2+,Ca)(MgFe2+)Si20 Clinopyroxene mineral species intermediate in composition between clinoenstatite and diopside, found in basic igneous rocks.
References in periodicals archive ?
Caption: FIGURE 4: The XRD patterns of spondyle clay (a) and MCSd-7 (b): F, augite Ca(Mg, Fe, Al)[[(Si, Al).sub.2][O.sub.6]]; G, pigeonite (Ca, Mg, Fe)(Mg, Fe)[Si.sub.2][O.sub.6]; C, quartz Si[O.sub.2]; M, magnetite [Fe.sub.3][O.sub.4].
Ca-poor pyroxene is inverted pigeonite. Weakly serpentinized olivine ([Fa.sub.35-44]) is more idiomorphic in gabbros than in anorthosites.
Low-Ca-pyroxene (pigeonite or Contain a low-Ca-pyroxene orthopyroxene) absent.
Various factors, including magma composition, control whether orthopyroxene or pigeonite occurs as the low-Ca pyroxene, but high temperatures yield orthopyroxene and low-pressure crystallization favours pigeonite.
Petrographically, the basalts are described as containing calcic plagioclase, augite, and rarer pigeonite and bronzite, and Fe-Ti oxides, and vary from holocrystalline to variably vitrophyric ([less than or equal to]30%).