CET/UWA Microstructure CourseCET/UWA Microstructure Coursegrain boundary geometry where triple junctions meet close to 120 degrees and all grain boundaries are straight or gently curved. IF IN THE EXAM YOU STATE THAT A PARTICULAR MICROSTRUCTURE SHOWS TRIPLE JUNCTIONS YOU WILL FAIL, HOWEVER IF YOU SAY THAT THE TRIPLE JUNCTIONS ARE AT 120 degrees OR SOME OTHER ANGLE, YOU MAY PASS.
showing large aspect ratios sitting in a finer grained, more equant matrix of same mineralogy. Can form by flattening of individual grains, grain boundary migration, coalescence of two grains with same orientation, or rotation of neighbouring grain's lattices into same orientation.
isolated (in 2D) set of grains with the same crystallographic orientation which were once part of same grain, but have been isolated by grain boundary migration. Grains A, B & C below all have the same crystallographic orientation mortar texture rock showing bimodal grain size distribution with large grains surrounded by a matrix of smaller grains.
originally old mining term meaning that the rock can be cleaved, ie it can be split into planar sheets, used for roofing tiles. The two most common types of cleavage are slaty cleavage and crenulation cleavage.
cleavage formed by reorientation of a previous cleavage. Occurs by a combination of micro-buckling, recrystallisation & mass transfer.
The preferred shape orientation distribution of grains in a rock.
Grain boundary alignment: The preferred alignment of grain boundaries in a rock,
which does not necessarily directly correlate with GSF.
CPO Crystallographic Preferred Orientation.
aka Lattice Preferred Orientation, texture, fabric, Orientation Distribution
Function. The orientation distribution of one or more crystal axes in a
rock.
Girdle: small or large circle distribution of crystal axes on a stereonet.
Point maxima: cluster of crystal axes around one orientation.
VIEPS Deformation Microstructures Course Lab 2 - Grain shape and crystallographic fabrics