Joints and Fractures Flashcards
Joints with patterns that are typically arranged in roughly hexagonal arrays that isolate columns of rock formed during the cooling of igneous rocks
Columnar Joints
Unfilled or filled joints that come in pair
Conjugate Joints
Through-going joints in continuous joints
Master Joints
Joints that do not share a common orientation and those with highly curved and irregular fracture surfaces
Nonsystematic Joints
Through-going joints that can be traced across an outcrop
Continuous Joints
Short joints that occur between the continuous joints
Cross Joints
Joints which trend at high angles (~60 to 90 degrees) to the regional bedding strike
Cross-strike Joints
Joints formed in a layer of mud when it dries and shrinks into roughly hexagonal plates
Desiccation Cracks
Short joints that terminate within an outcrop, generally at the intersection with another joint
Discontinuous Joints
Set of joints that roughly parallels ground surface topography and whose spacing decreases progressively toward the surface
Exfoliation Joints
Pre-existing microcracks and flaws in a rock, which include grain-scale fractures, pores and grain boundaries
Griffith Cracks
Joints that form at depth in response to abnormal fluid pressure and involving hydrofracturing
Hydraulic Joints
Joints that share a similar orientation in the same area
Joint Set
Two or more joint set in the same area
Joint System
Joints that merge with the fault and are inclined at an angle around 30 to 40 degrees to the fault surface
Pinnate joints
Joints that exhibit feathered structure
Plumose Joints
Joints that form late in history of an area and are ultimately oriented perpendicular to the original tectonic compression that formed from the dominant fabric in the rock
Release Joints
Joints which parallel the general strike of bedding
Strike-parallel Joints
Joints that have subparallel orientation and regular spacing
Systematic Joints
Joints that form at depth (<3km) with stress originating tectonically and horizontal compaction occurs
Tectonic joints
Joints that form because of the lack of shear involved
Tensile fractures
Joints that form when more than half of the original overburden have been removed from a rock mass
Unloading Joints
Joints filled with minerals or aggregates
Veins
New tensile cracks that spawn from propagating shear-mode cracks
Wing cracks
