OCTAHEDRON-- The octahedron is a form composed of 8 equilateral triangles. These triangle-shaped faces intersect all 3 crystallographic axes at the same distance, thus the form notation of {111} (fig. 3.3).
OCTAHEDRON:
Minerals like magnetite, chromite, franklinite, spinel, pyrochlore, cuprite, gold, and diamond fall in this group.
DODECAHEDRON: ...
Octahedron
An eight-sided geometric solid and one of the forms in the Isometric Crystal System. The most common crystal in which diamonds occur.
Opalescence
Milky or pearly appearance. Girasol.
OCTAHEDRON. Two four-sided pyramids united base to base.
OFF COLOUR. Having but a tint of desirable colour.
OLD MINE. Diamonds from the old Brazilian fields; old cut diamonds of good colour.
Octahedron: A crystal bounded by eight faces, like two pyramids joined at their bases. Diamond often crystallizes as an octahedron.
octahedron See octahedral crystal.
off-grain A diamond cutter must polish a diamond perpendicular to a single grain at all times during the faceting process to allow material removal and a high polish. This is referred to as on grain.
Octahedron
A solid figure having eight sides or faces. A rough diamond with this approximate shape. The commonest crystal formation of diamond.
Off Made, Off Make ...
Octahedron Inclusion with Angular Strain Feathers
Cloud Inclusion Under UV Light
Strain Feather 'Crashing Wave' Daimond Inclusion ...
Octahedron
Most common form of rough diamonds. Try to picture a small pyramid one on top of another, base to base for a general idea of this crystal structure. It is the best shape of rough for cutting brilliant cut diamonds.
Old European Cut ...
The octahedron form represents the merging of the physical, mental, and spiritual planes, thus symbolizing a state of completion.
20.0mm Octahedron Cut
[N] Not enhanced.
Quantity Available: 6
med violet-blue Fluorite$ 4.99 ...
A natural octahedron
by Rob Lavinsky, iRocks.com - CC-BY-SA-3.0
Diamonds crystallize in various forms of which the octahedral and dodecahedral crystals are the two most common ones.
cubic (cubes, octahedrons, often twinned)
Envronment:
pegmatites, high temperature to low temperature hydrothermal veins, replacements in chalks ...
Fig 22 Diamond octahedron showing tension cracks (20 x)
Feathers
-All types of cracks which are perpendicular to the crack plane and appear white and feathery are termed "feathers" or "glets".
Crystallography: cubic, tetragonal trisoctahedron (trapezohedron) transparent to translucent
Colors: colorless, white, greenish, reddish
Luster: glassy
Hardness: 5 to 5.5
Fracture: subconchoidal
Specific gravity: 2.3
Cleavage: traces of cubic ...
tetragonal trisoctahedron Synonym of trisoctahedron. texture The feel and appearance of a mineral, such as color, crystal form, and luster.
They occur in nature as eight-sided crystals known as octahedrons (eight faces). To best use their natural form and unique optical properties, they are commonly fashioned into the 58-facet cut known as the modern round brilliant.
Crystals of the cubic system: a cube (e.g., pyrite) at left, and an octahedron (e.g., diamond) at right. Note the three crystallographic axes, which meet in the center, are of equal length.
90 carats; multi-faceted octahedron; cape
5 - 114.28 carats; high (old) cushion brilliant; silver cape
6 - 86.61 carats; rounded triangular brilliant; cape
7 - 86.28 carats; irregular Mogul cut; silver cape
8 - 78.
These include the hexoctahedron, gyroid, hextetrahedron, diploid, and tetartoid, among others.
The Oppenheimer Diamond is a perfect octahedron. It is the common shape which most of the earth's natural diamonds have. In fact the Oppenheimer Diamond has also been regarded as one of the huge crystals in the world.
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.
It is still preferred when the raw crystal is in an octahedron formation. Even though as much as 50% of the stone is cut away in the process, often two stones can be carved from an octahedron.
Octahedron - An eight-sided crystal of the Isometric System (Diamond, Pyrite)
Oolitic - Habit made up of small rounded grains (oolites)
Opalescence, Opalescent - Showing an internal play of colors or iridescence. (Opal) ...
The material below has been cut into a geometric form known as a "cuboctahedron" from synthetic rutile (which has extreme birefringence = .287). It has been placed above a single black ink dot on the surface.
It is a huge, semi-polished octahedron. Sitwell (1953) states that the stone is backed by a gold foil, as were many ancient gems, to improve its brilliance. This has not been removed for fear of damaging the gem.
Common forms in the cubic system are the tetrahedron (4 faces), the cube (6 faces), the octahedron (8 faces), the dodecadehedron (12 faces), the trapezohedron (24 faces), and the hexoctahedron (48 faces).
He reported that huge, translucent, purplish pink octahedrons ( 'le rubis balais' ) over 20 cm in size were extracted at that locality. Almandine garnet was said to occur on the left bank.
This is because the four sided pyramid shape of the princess cut diamond is similar to one half of the octahedron rough stone from which a princess diamond is cut.
The peridot is cut in accordance with its crystal shape, mostly faceted or in classical table cuts, or round, antique, as an octahedron or oval. Smaller crystals are cut into standardised series stones, larger ones into imaginative one-offs.
In form the crystal is a combination of the tetragonal trisoctahedron (trapezohedron), the predominating form, with the dodecahedron and the hexoctahedron.
The internal structure of a diamond (usually as octahedron, tetrahedron, cube or rhombic dodecahedron) that has a direct influence on its external morphology.
Culet ...
Compared to a Round Brilliant, a cutter can retain more of the original crystal when cutting an octahedron into a Princess shape. The square corners of the rough need to be cut away to create a Round, but they are saved when cutting a Princess.
Gem Crystals Indeed II: Tanzanian spinel in a strawberry-colored octahedron; an unusual Burmese lavender spinel; short and stocky Brazilian imperial topaz. (Photo: Jason Stephenson) ...
The most powerful stones were thought to be naturally occurring octahedrons of exceptional clarity that exhibited fire. These stones would bring the owner power, wealth, everlasting youth and good fortune.
Spread Stone - A term that is used frequently in the diamond trade to refer to a stone that has been cut with a large table and a thin crown, to retain greater weight from the two sawn pieces of an octahedron than is possible by using ideal ...
A diamond crystal is composed of an enormous number of cubic unit cells that are stacked to produce crystal faces. Stacking of cubes to produce an octahedron, a common diamond crystal shape, is shown above.
Illustrations constructed with XTALDRAW ...
from different hardness-testing methods, but also from the fact that various directions on a given stone's surface show a considerable variation in resistance to abrasion. The hardest direction in diamond is parallel to the faces of the octahedron.
Spinel typically forms in well formed octahedrons. But it is famous for a type of twinning that bears its name, the Spinel Twin Law. Spinel is not a synthetic stone. It is a real, natural, attractive and rare gemstone in its own right.
 See also: Crystal, Diamond, Shape, Stone, Color
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