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Influence of grinding on graphite crystallinity from experimental and natural data: implications for graphite thermometry and sample preparation

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Crespo Feo, Elena and Luque del Villar, Francisco Javier and Fernández Barrenechea, José María and Rodas, Magdalena (2006) Influence of grinding on graphite crystallinity from experimental and natural data: implications for graphite thermometry and sample preparation. Mineralogical magazine, 70 (6). pp. 697-707. ISSN 0026-461X

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Official URL: http://minmag.geoscienceworld.org/



Abstract

This paper examines the effects of shear stress on the structuralparameters that define the
‘crystallinity’ of graphite. The results show that highly crystalline graphite samples ground for up to
120 min do not undergo detectable changes in the three-dimensional arrangement of carbon layers but
crystallite sizes (Lc and La) decrease consistently with increasing grinding time. Grinding also involves
particle-size diminution that results in lower temperatures for the beginning of combustion and
exothermic maxima in the differentialthermalanal ysis curves. These changes in the structuraland
thermalcharacteristics of graphite upon grinding must be taken into account when such data are used
for geothermometric estimations.
Tectonic shear stress also induces reduction of the particle size and the Lc and La values of highly
crystalline graphite. Thus, the temperature of formation of graphite according to structural as well as
thermaldata is underestimated by up to 100ºC in samples that underwent the most intense shear stress.
Therefore, application of graphite geothermometry to fluid-deposited veins where graphite is the only
mineralfound should take into consideration the effect of tectonic shearing, or the estimated
temperatures must be considered as minimum temperatures of formation only.


Item Type:Article
Uncontrolled Keywords:Graphite, Shear stress, Grinding, Crystallinity, Geothermometry
Subjects:Sciences > Geology > Crystallography
Sciences > Geology > Mineralogy
ID Code:17607
Deposited On:10 Jan 2013 09:09
Last Modified:11 Dec 2018 08:46

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