International Geologiical Congress - Oslo 2008


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MPM-13 Inclusions in minerals


TEM study of star garnet from Idaho: Implication to the origin of oriented rutile needles in garnet of metamorphic rocks


Hao-Tsu Chu, Central Geologcial Survey (Taiwan)
Shyh-Lung Hwang, Department of Materials Science Engineering, National Dong Hwa University (Taiwan)
Pouyan Shen, Institute of Materials Science and Engineering, National Sun Yat-sen University (Taiwan)
Tzen-Fu Yui, Institute of Earth Sciences, Academia Sinica (Taiwan)


The <100>grt aligned rutile needles follow <100>grt/<001>rt with well developed {110}grt/{100}rt and {100}grt/{110}rt interfaces. The <111>grt aligned needles follow <111>grt//<103>rt with {100}rt parallel to either {112}grt or {110}grt, the latter relationship being energetically most favorable in terms of lattice mismatch.
These crystallographic data, along with the garnet growth sectors with rutile grouping into trails oriented along <110>grt behind the garnet crystal faces as revealed by optical microscopy, suggesting that rutile needles in star garnets were most likely formed through an epitaxial deposition / intergrowth mechanism at garnet growth fronts. This knowledge sheds light on the formation of rutile needles in garnet in metamorphic rocks..


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