Skip to Main Content
GEOREF RECORD

Morphology and microstructure of magnetite and ilmenite inclusions in plagioclase from Adirondack anorthositic gneiss

Hans-Rudolf Wenk, Kai Chen and Rebecca Smith
Morphology and microstructure of magnetite and ilmenite inclusions in plagioclase from Adirondack anorthositic gneiss
American Mineralogist (August 2011) 96 (8-9): 1316-1324

Abstract

It is well known that oriented iron and titanium oxide inclusions occur in pyroxenes and plagioclase of anorthosites and granulites, and they are attributed to exsolution at subsolidus conditions. The oxides occur as needles or platelets. In this study, we determine the morphology of oxide needles as well as their orientation in plagioclase (An 30-35) in anorthosite gneiss from the Adirondack mountains (New York). The investigation was done with electron backscatter diffraction (EBSD) in a scanning electron microscope, as well as Laue diffraction with a microfocus synchrotron X-ray beam at the Advanced Light Source in Berkeley. It was observed that the needle direction is [110] in magnetite and [1010] in ilmenite. The needle direction is consistently parallel to [001] of plagioclase. Furthermore, (111) of magnetite and (0001) of ilmenite are sub-parallel to (120) and (120) of plagioclase. We note that for directions [110] in the magnetite structure and 1010 in ilmenite, O atoms are close-packed, and (111) and (0001) are close-packed planes, correspondingly. In plagioclase, [001] is a direction with open channels as well as approximate alignment of Si tetrahedral edges, thus providing nucleation sites with a coincidence lattice relationship. (120) and (120) in this triclinic mineral are planes with approximate tetrahedral sides so that the relationship is structurally plausible. From Laue diffraction, we can determine that the magnetite needle axis is subject to an extensional stress, most likely attained during cooling of the inclusions within the plagioclase host.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 96
Serial Issue: 8-9
Title: Morphology and microstructure of magnetite and ilmenite inclusions in plagioclase from Adirondack anorthositic gneiss
Affiliation: University of California at Berkeley, Department of Earth and Planetary Science, Berkeley, CA, United States
Pages: 1316-1324
Published: 201108
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 39
Accession Number: 2011-076474
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
N43°00'00" - N44°30'00", W75°00'00" - W73°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201142
Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal