Cleavage, in geology and related disciplines, describes the tendency of a mineral or rock to break along preferred planes of weakness. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific
Cleavage in mineralogy
Minerals cleave along particular crystallographic planes along which bonds are comparatively weak. Cleavage, in Mineralogy, is the tendency of crystalline materials to split along definite planes creating smooth surfaces of which there are several named types The number of cleavage planes and the angles between them are a characteristic of a particular mineral. Minerals can have from one up to five cleavage planes e. g. micas have a single plane of cleavage while galena has three cleavages at 90° to each other. The word "mica" is thought to be derived from the Latin word la micare, "glitteren" in reference to the brilliant appearance of this mineral (especially Galena is the natural mineral form of Lead sulfide. It is the most important Lead Ore mineral The quality of the cleavage is also important in identifying minerals and is described both in terms relative to a perfectly planar cleavage (perfect, imperfect, distinct, good, fair, and poor) and the difficulty of getting the mineral to cleave (easy, hard and difficult).
Some minerals do not have any cleavage and break unevenly. This is called fracture e. A fracture is any local separation or discontinuity plane in a Geologic formation, such as a joint or a fault that divides the rock into two or more g. quartz exhibits a conchoidal fracture. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in
Cleavage in structural geology
Rocks deformed under very low to low metamorphic grade often develop planes along which the rock can easily be split. Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i Slates are an example of a rock with a penetrative cleavage caused partly by the realignement of phyllosilicate minerals with increasing flattening strain. Slate is a fine-grained foliated homogeneous, Metamorphic rock derived from an original Shale -type Sedimentary rock composed of Clay The silicate minerals make up the largest and most important class of rock-forming Minerals They are classified based on the structure of their silicate Ion group
With increasing metamorphic grade and growth of new minerals, penetrative cleavage grades into a foliation. Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic
See also
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