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Rhombohedral cleavage occurs when there are three cleavage planes intersecting at angles that are not 90 degrees. Calcite has rhombohedral cleavage. Octahedral cleavage occurs when there are four cleavage planes in a crystal. Fluorite exhibits perfect octahedral cleavage. Octahedral cleavage is common for semiconductors.
Fluorite has four perfect cleavage planes that help produce octahedral fragments. [14] The structural motif adopted by fluorite is so common that the motif is called the fluorite structure . Element substitution for the calcium cation often includes strontium and certain rare-earth elements (REE), such as yttrium and cerium .
The fluorite structure refers to a common motif for compounds with the formula MX 2. [1] [2] The X ions occupy the eight tetrahedral interstitial sites whereas M ions occupy the regular sites of a face-centered cubic (FCC) structure. Many compounds, notably the common mineral fluorite (CaF 2), adopt this structure.
Octahedral cleavage (four directions) is present in fluorite and diamond, and sphalerite has six-directional dodecahedral cleavage. [ 82 ] [ 83 ] Minerals with many cleavages might not break equally well in all of the directions; for example, calcite has good cleavage in three directions, but gypsum has perfect cleavage in one direction, and ...
A category for compounds with the same crystal structure as calcium fluoride (fluorite), or the structure of magnesium silicide (anti-fluorite). This category is also known by the Strukturbericht designation C1, and falls under the space group Fm 3 m (No. 225).
Smoky quartz with spessartine on top of feldspar matrix, featuring different crystal habits (shapes). In mineralogy, crystal habit is the characteristic external shape of an individual crystal or aggregate of crystals.
Since the nature of cleavage is dependent on scale, slaty cleavage is defined as having 0.01 mm or less of space occurring between layers. [1] Slaty cleavage often occurs after diagenesis and is the first cleavage feature to form after deformation begins. The tectonic strain must be enough to allow a new strong foliation to form, i.e. slaty ...
These groups may contain only two-fold axes, mirror planes, and/or an inversion center. These are the crystallographic point groups 1 and 1 (triclinic crystal system), 2, m, and 2 / m (), and 222, 2 / m 2 / m 2 / m , and mm2 (orthorhombic).