Search results
Results From The WOW.Com Content Network
Tensile cracks, also referred to as wing cracks (red) grow at an angle from the edges of the shear fracture allowing the shear fracture to propagate by the coalescing of these tensile fractures. Cracks in rock do not form smooth path like a crack in a car windshield or a highly ductile crack like a ripped plastic grocery bag.
Microcracks in rock, also known as microfractures and cracks, [1] are spaces in rock with the longest length of 1000 μm and the other two dimensions of 10 μm. In general, the ratio of width to length of microcracks is between 10 −3 to 10 −5 .
If the tensile stress exceeds the magnitude of the least principal compressive stress the rock will fail in a brittle manner and these cracks propagate in a process called hydraulic fracturing. Hydraulic joints occur as both nonsystematic and systematic joints, including orthogonal and conjugate joint sets.
The radiating cracks sometimes intersect a second set of concentric cracks. [36] [34] However, the cracks can be highly variable in shape and volume, as well as the degree of shrinkage they indicate. [37] The matrix is typically composed of argillaceous carbonate, such as clay ironstone, while the crack filling is usually calcite.
A newly formed fracture leads to changes in the stress field and tensile strength of the fractured rock and causes a drop in stress magnitude. If a stress increases again, a new fracture will most likely be generated along the same fracture plane. This process is known as the crack-seal mechanism [6]
Tensile cracks can form in a compressive stress field due to the influence of pervasive microcracks in the rock lattice and extension of so-called wing cracks from near the tips of preferentially oriented microcracks, which then curve and align with the direction of the principle compressive stress.
The mudcracked rock is then later exposed to erosion. [2] In these cases, the original mud cracks will erode faster than the newer material that fills the spaces. This type of mudcrack is used by geologists to determine the vertical orientation of rock samples that have been altered through folding or faulting. [13]
Columnar jointing in Giant's Causeway in Northern Ireland Columnar jointing in the Alcantara Gorge, Sicily. Columnar jointing is a geological structure where sets of intersecting closely spaced fractures, referred to as joints, result in the formation of a regular array of polygonal prisms (basalt prisms), or columns.