Three-dimensional Fabric Analysis of Microcracks associated with Brittle Failure of Granitic Rocks.

Surface features of uniaxial tensile fractures and their relation to rock anisotropy in Inada granite

“…Fig. 10a shows a contour plots of poles to microcracks observed by using a universal-stage in Inada granite [13]. The microcracks (n ¼ 1868) are composed of intraquartz (n ¼ 1314), intrafeldspar (n ¼ 300) and grain-boundary cracks (n ¼ 254).…”

“…Almost all of them are intragranular and grain-boundary (intergrain) cracks, and transgranular ones are very rare. Mean length of microcracks are about 1 mm for both intragrain and grain-boundary cracks [13,16]. The area crack density, r A;X i (mm/mm 2 ), defined as the total trace length divided by the observed area, changes considerably depending on the orientation of the observed X i plane; i.e., r A;X 1 ¼ 0:80, r A;X 2 ¼ 0:95, r A;X 3 ¼ 1:14 [13,16,17].…”

“…The area crack density, r A;X i (mm/mm 2 ), defined as the total trace length divided by the observed area, changes considerably depending on the orientation of the observed X i plane; i.e., r A;X 1 ¼ 0:80, r A;X 2 ¼ 0:95, r A;X 3 ¼ 1:14 [13,16,17]. About 70% of the crack density is occupied by intraquartz cracks, and the rest by intrafeldspar and grain-boundary cracks in all directions [13].…”

“…The granite consists of quartz (37% v/v), potassium feldspar (24%), plagioclase (33%), biotite and others (6%) [13]. These normative mineral ratios are calculated from the chemical composition of the granite.…”

“…1). For convenience, three orthogonal directions normal to these planes were taken as reference axes x i (i ¼ 1; 2; 3), and a plane normal to a reference axis x i is called the X i plane [13,16]. Under microscope, the minerals are almost randomly distributed in each thin section parallel to the X i plane (Fig.…”