Quantification of inhomogeneity in mechanical properties of rocks in nanometer scale

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We investigated how quartz single crystal deformes around the indentation impression by using the Raman microspectroscopy and the EBSD-SEM.The laser Raman microspectroscopy revealed that quartz far from the indentation impression exhibit clear Raman spectra with strong bands at wavenumbers of 728. 206 and 464 cm-7 which are typical for intact a-quartz. The clear bands gradually shift and broaden with approaching to the indentation impression. They have shoulders at the edge of the impression, and finally split into two subbands at the central part of the impression. Such shape change of the Raman bands is considered to be related to the generated residual stress field within the quartz crystal by the indentation test. The magnitude of the residual stress can be estimated from the shifted wavenumbers of the Raman bands, and the maximum compressive and tensile stresses are revealed to exceed 2 and 0.1 GPa, respectively, at the center of the indentation impression.The SEM-EBSD study revealed that Dauphine twins can be perceived with the characteristic Kikuchi bands and contrasts in the back scattered images in hexagonal areas close to the indentation impression. As Dauphine twins occur systematically with respect to the indented impression, we concluded that Dauphine twins have developed during the indentation test.