World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0004167941
Reproduction Date:

Title: Pigeonite  
Author: World Heritage Encyclopedia
Language: English
Subject: Ureilite, Pyroxene, Ultra-high-temperature metamorphism, Northwest Africa 7034, Yamato 691
Collection: Calcium Minerals, Iron Minerals, Magnesium Minerals, Pyroxene Group
Publisher: World Heritage Encyclopedia


Polarized light microscope image of part of a grain of orthopyroxene containing exsolution lamellae of augite The texture documents a multistage history: (1) crystallization of twinned pigeonite, followed by exsolution of augite; (2) breakdown of pigeonite to orthopyroxene plus augite; (3) exsolution of augite parallel to the former twin plane of pigeonite. (long dimension 0.5 mm, Bushveld igneous complex)
Category Silicate mineral Pyroxene
(repeating unit)
Strunz classification 09.DA.10
Dana classification
Crystal symmetry Monoclinic prismatic
H-M symbol: (2/m)
Space group: P 21/c
Unit cell a = 9.7 Å, b = 8.95 Å, c = 5.24 Å; β = 108.59°; Z = 4
Color Brown, greenish brown-black
Crystal habit Prismatic crystals, to 1 cm; granular, massive.
Crystal system Monoclinic
Twinning Commonly twinned simply or multiply on {100} or {001}
Cleavage Good on {110}, (110) ^ (110) ~87°
Fracture Conchoidal
Tenacity Brittle
Mohs scale hardness 6
Luster Vitreous to dull
Streak Grey white
Diaphaneity Semitransparent
Specific gravity 3.17 - 3.46 measured
Optical properties Biaxial (+)
Refractive index nα = 1.683 - 1.722 nβ = 1.684 - 1.722 nγ = 1.704 - 1.752
Birefringence δ = 0.021 - 0.030
Pleochroism Weak to moderate; X = colorless, pale green, brown; Y = pale brown, pale brownish green, brownish pink; Z = colorless, pale green, pale yellow
2V angle 0 - 30° measured
Dispersion weak to distinct
References [1][2][3]

Pigeonite is a mineral in the clinopyroxene group. It has a general formula of (Ca,Mg,Fe)(Mg,Fe)Si2O6. The calcium cation fraction can vary from 5% to 25%, with iron and magnesium making up the rest of the cations.

Pigeonite crystallizes in the monoclinic system, as does augite, and a miscibility gap exists between the two minerals. At lower temperatures, pigeonite is unstable relative to augite plus orthopyroxene. The low-temperature limit of pigeonite stability depends upon Fe/Mg ratio in the mineral and is hotter for more Mg-rich compositions; for a Fe/Mg ratio of about 1, the temperature is about 900 °C. The presence of pigeonite in an igneous rock thus provides evidence for the crystallization temperature of the magma, and hence indirectly for the water content of that magma.

Pigeonite is found as phenocrysts in volcanic rocks on Earth and as crystals in meteorites from Mars and the Moon. In slowly cooled intrusive igneous rocks, pigeonite is rarely preserved, but textural evidence of its breakdown to orthopyroxene plus augite may be present, as shown in the accompanying microscopic image.

Pigeonite is named for its type locality on Lake Superior's shores at Pigeon Point, Minnesota, United States. It was first described in 1900.[3]


  1. ^ Handbook of Mineralogy
  2. ^ Webmineral data
  3. ^ a b
This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.