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Because rocks are essentially aggregates of minerals, we can think of them as poly-crystalline materials. Dislocations are a type of crystallographic defect which consists of an extra or missing half plane of atoms in the periodic array of atoms that make up a crystal lattice.
Dislocation creep is a non-linear (plastic) deformation mechanism in which vacancies in the crystal glide and climb past obstruction sites within the crystal lattice. [1] These migrations within the crystal lattice can occur in one or more directions and are triggered by the effects of increased differential stress .
In metamorphic rocks that experience deformation during metamorphism, porphyroblasts may grow before, during, or after the phase of deformation recorded by the matrix minerals. The relationship of porphyroblast growth to deformation is typically evaluated by comparing the shape orientation of trails of mineral inclusions in the porphyroblast to ...
In metamorphic rocks, coesite is now recognized as one of the best mineral indicators of metamorphism at very high pressures (UHP, or ultrahigh-pressure metamorphism). [8] Such UHP metamorphic rocks record subduction or continental collisions in which crustal rocks are carried to depths of 70 km (43 mi) or more. Coesite is formed at pressures ...
In geology, shear is the response of a rock to deformation usually by compressive stress and forms particular textures. Shear can be homogeneous or non-homogeneous, and may be pure shear or simple shear. Study of geological shear is related to the study of structural geology, rock microstructure or rock texture and fault mechanics.
The equations that govern the deformation of jointed rocks are the same as those used to describe the motion of a continuum: [13] ˙ + = ˙ = = ˙: + = where (,) is the mass density, ˙ is the material time derivative of , (,) = ˙ (,) is the particle velocity, is the particle displacement, ˙ is the material time derivative of , (,) is the Cauchy stress tensor, (,) is the body force density ...
Mylonite is a fine-grained, compact metamorphic rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. Mylonites can have many different mineralogical compositions; it is a classification based on the textural appearance of the rock.
Phosphorite – Sedimentary rock containing large amounts of phosphate minerals – A non-detrital sedimentary rock that contains high amounts of phosphate minerals; Sandstone – Type of sedimentary rock; Shale – Fine-grained, clastic sedimentary rock; Siltstone – Sedimentary rock which has a grain size in the silt range