Octahedral: A geometric object with eight plane surfaces.
Oiling: The process of applying mineral oil to a stone, such as an emerald, to mask inclusions and enhance the color.
octahedral crystal A well shaped diamond crystal which has a symmetrical layout of eight equilateral triangles. It has the appearance of two pyramids joined at the bases. Also referred to as an octahedron.
13. Octahedral Crystal Habit
Octahedral White Spinel (center), Diamond Rough (right)
14. Pincoid Crystal Habit ...
Octahedral, Dodecahedral, or Rhombohedral cleavage: cleavage parallel to the faces of an octahedron, dodecahedron, or rhombohedron (respectively). Octahedral cleavage is seen in common semiconductors (see below).
(Octahedral crystal)
Pure Carbon
A diamond is composed of almost pure carbon, one of the Earth's most common substances, just like graphite and pencil lead. But...
Perfect octahedral crystals are sometimes set into jewelry in their original uncut octahedral shapes. The Burmese refer to these gems as nat thwe, meaning spirit polished. Sometimes nat thwe spinels will receive a very light polishing.
Figure 8. Octahedral diamond crystal, 2.6 cm, from Mbuji-Mayi, Congo. Crystal Classics specimen; Jeff Scovil photo.
Isometric; octahedral, dodecahedral, cubic ...often distorted as nuggets
Envronment:
veins in hydrothermal deposits, and hydrothermal replacements ...
Due to the octahedral nature of spinel rough, the most common shape seen is the cushion
Rounds are also seen, as are other shapes, such as the emerald cut
(click on colour to find other gemstones)
TREATMENTS ...
[Natural octahedral spinel crystal, spinel crystals in their site of formation: white calcite marble] ...
GLASSIES. Octahedral diamond crystals (transparent).
GLASSY. Applied to diamonds which lack brilliancy.
Just like the trisoctahedral form, this form is most often seen on diamond, where it is thought to represent a solution form derived from an octahedron, not true crystallization.
Cleavage: perfect, octahedral (4 directions)
Specific Gravity: 3.514 - 3.518
R.I.: 2.4175 in sodium light; one of the highest R.I.s of any gem material.
It forms octahedral crystals (ISOMETRIC SYSTEM) and granular masses that are various shades of red; parallel, elongated ruby -red needles are called chalcotrichite, and brick - red earthy masses are called tile ore.
octahedral cleavage Type of cleavage exhibited on minerals of the isometric system that crystallize as octahedrons. The method of cleavage is that flat, triangular "wedges" peel off of the existing octahedron. Example is Fluorite.
Individual copper crystals may may be of cubic, dodecahedral, tetrahedral, and very rarely of octahedral shape. Aggregates of crystals may be wiry in habit or form a dendritic, arborescent branching structure.
The hardness attribute of diamonds vary with the direction in the crystal, the hardest direction being normal to the octahedral face. Diamonds have a conchoidal fracture.
Spinel is a very hard semi-precious stone composed of octahedral crystals. Spinel ranges in color from red to black to yellow, frequently resembling rubies. Iron and chrome are components of spinel, giving it its color.
However, with the use of diamonds in jewelry, sometime in the 13th century it became known that a diamond's appearance could be enhanced by grinding and polishing [later by cleavage (below)] along the four octahedral faces (below) of the ...
Hard as it is, diamond splits readily in certain definite directions (parallel to any of the triangular faces of the octahedral crystal).
Diamonds crystallize in various forms of which the octahedral and dodecahedral crystals are the two most common ones. These natural crystals have been adorned in their own right for millennia.
this young guy was taking his first GIA Diamonds course and had just learned that a trigon would only be found on a natural diamond, and would be connected to the dodecahedral surface of the octahedral crystal formation.
The early years of the South African diamond mining industry certainly witnessed the appearance, in unheard of numbers, of large yellow crystals, many of them octahedral in shape.
Cube - One of the seven basic forms in the highest symmetry (hexoctahedral) class of the cubic, or isometric, crystal system.
Spinel: Probably named from the Latin word "spina", (meaning "thorn"), for its pointed crystals, spinel is a hard mineral with octahedral crystals occurring in igneous and carbonate rocks.
Diamonds can be cut and polished only with other diamonds, and only because of slight directional differences in hardness and a perfect octahedral cleavage. While diamonds are tough, they can be chipped along sharp girdles or facet edges.
GALENA - Leadhills.
Intergrown cubo-octahedral xtls. to 2cms.
CALCITE - New Glencrieff Mine, Wanlockhead.
A 25mm scalenohedral crystal speckled with pyrite crystal inclusions.
These occur in the direction of the cleavage planes parallel to the four octahedral faces. They always occur in straight lines and the cleavage plane often shows a fine striation, similar to that of a cleaved piece of wood (Fig 15).
Danalite: A mineral that occurs in octahedral crystals that is reddish in color.
Dangle Earring: An earring that dangles below the ear lobe.
Dark Stone: A rhinestone that has turned black or dark gray in color.
A simple, obsolete cut with one "slice" cleaved or polished from (usually) an octahedral. forming a table as on a modern stone.
Table Facet
The top and largest facet on most diamonds including brilliant cuts.
Diamonds fashioned in the round shape with 58 facets. It is the most efficient cut for diamonds cut from octahedral rough.
Canary Diamond
Trade name for a yellow diamond with very intense yellow/green or yellow/orange color.
This is due to the fact that the best crystals often occur in flattened octahedral and twinned stones.
Due to the absence of color zoning and dichroism in spinels, recutting them is not a difficult task and is often worth while.
Danalite: A reddish mineral composed of iron, zinc manganese, glucinum and sulphur occurring in massive octahedral crystals. Danalite is named after James Dwight Dana.
There is abundant evidence that the premature years of the South African diamond mining industry witnessed the emergence of large yellow crystals that were octahedral in shape.
Crystal Habit
Crystal Habit is a consistent pattern that certain solids form. Common examples include Acicular, Dodecahedral, Octahedral, Platy, Prismatic, and Tabular.
The Black Prince's Ruby is really a large, semi-polished octahedral Spinel. The stone measures two inches in length and is of proportionate width. The exact weight of the gemstone is unknown but estimates put it at approximately 170 carats.
" It may be quite tough but easily scratched, or it may be exceedingly hard but lack toughness because of easy cleavage. Diamond is highest on the scale of hardness and, despite it rather easily developed octahedral cleavage, ...
Dana, we are told that garnets “crystallize in the hex octahedral class of the isometric crystal system.' The most common crystal habits for this class are the cube and the octahedron.
crystal arrangement is one in which the crystal essentially expands outward at the same rate in all directions during its initial growth; the ideal result, when the crystal forms without any interference, is a pure and perfectly formed octahedral ...
 See also: Crystal, Diamond, Stone, Shape, Mineral
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