DODECAHEDRON (AKA Rhombic Dodecahedron) -- This form is composed of 12 rhomb-shaped faces (fig. 3.4). Each of these rhomb-shaped faces intersects two of the axes at equidistance and is parallel to the 3rd axis, thus the notation {011}.
DODECAHEDRON:
Magnetite and sodalite are placed in this category.
TETRAHEXAHEDRON: ...
Dodecahedron
A twelve-sided geometric solid. One of the crystal forms found in the Isometric crystal system.
DODECAHEDRON. A geometrical form in the isometric or cubic system applied to crystallography; a solid figure of twelve equal sides, each a regular pentagon--of five equal sides and angles.
Dodecahedron - One of the seven basic forms in the highest symmetry (hexoctahedral) class of the cubic, or isometric, crystal system.
Isometric (dodecahedrons and trapezohedrons common)
Envronment:
hydrothermal metamorphics, and plutonic rocks ...
rhombic dodecahedron See dodecahedron rhombohedral clevage Type of cleavage exhibited on minerals that crystallize in the hexagonal system and as rhombohedrons, in which small rhombohedrons cleave off of the existing rhombohedron.
The dodecahedral form is so typical that the dodecahedron was once known as a garnetohedron. Richard M. Pearl states in his Garnet, Gem and Mineral that “Twinning of garnet crystals shows only in the effect of double refraction.
Spheres are initially sawed into cubes or dodecahedrons and then ground to shape between two pipes or rotating concave cutters, allowing the stone to rotate freely in any direction to form a perfect spherical shape.
As diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, octahedron, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron.
The largest found thus far, a well formed dodecahedron imbedded in calcite, was collected in 1964 by Pierre Bariand, mineral collection curator at The Sorbonne.
Lazurite gem deposits occur in white and black marbles hundreds of meters thick.
The rhombic dodecahedronic structure makes it exceptional. Miners face a lot of problem while mining this gemstone as it is repeatedly confused with minerals like tetrahedrite, galena and acanthite. Sometimes it shows striations.
Left: the top view of a dodecahedron. Right: the top of a French cut
The basic design of a French cut.
If six directions are perfectly cleaved on a single crystal, it forms rhombic dodecahedron. However, identifying the six directions in a single piece is quite difficult because of multiple twinning and the many directions.
[Idealized drawing of a rhombic dodecahedron, a classic Uvarovite crystal habit] ...
Dodecahedron - A twelve-sided crystal in the Isometric system.
Dome - A crystal form parallel to one of the lateral axes and intersecting the other two.
The internal structure of a diamond (usually as octahedron, tetrahedron, cube or rhombic dodecahedron) that has a direct influence on its external morphology.
Culet ...
Hexahedron (Pyrite)
Octahedron (Diamond, Spinel)
Tetrahedron (Tetrahedrite)
Dodecahedron (Rhombic - Garnet)
Hexoctahedron (Diamond) ...
In form the crystal is a combination of the 2-2 tetragonal trisoctahedron (trapezohedron), the predominating form, and I-dodecahedron, and 34 hexoctahedron.
It looks similar to Lapis, and is a component of Lapis, occurring in massive dodecahedrons and found in igneous rocks. It has varying degrees of white veins of calcite and an occasional speck of pyrite.
Of the six types of crystals only five are large enough to be used in jewelry. The garnet crystals form in a cubic system with a twelve-faced rhombic dodecahedron and the twenty four faced icostetrahedron and in combinations of these two forms.
Garnet crystals form in the cubic system, typically as a 12-sided crystal or dodecahedron. They are available in all colors except pure Blue. One problem with some types of garnets comes from their deeply saturated color.
 See also: Crystal, Mineral, Diamond, Crystals, Gemstones
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