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Gandhara Gemstones is one of the well-known sources for supplying rough gemstones from all over the world, we often travel directly to the mines to find the best stones and have friendly ties with mine owners in countries such as Pakistan, Afghanistan, South Africa, Thailand, and Cambodia. We also secure stones from trusted suppliers worldwide.
We take pride in displaying our finest rough gemstones collection for enthusiasts around the world, that is why Gandhara Gemstones has dedicated a section for rough gemstones. Please take a look at all we have to offer in this section!
A gem is a precious or semiprecious stone that has been cut, polished, or otherwise modified to be used as personal insignia or as decoration.
Rough Gemstones / Raw Gemstones
A gemstone in its natural form that has not yet been polished or cut just like they were made by mother nature. They are referred to as raw gems but the most formal name is rough gemstones.
Rough Gemstones Evaluation
Good Color, Good Shape, Good Size and Good Clarity are normal desirable traits in rough gemstones.
Color of Rough Gemstones:
The eye will automatically find the most expensive stones because of its exquisite color. Color is the key in any gemstone that is colored around 60% or more, so look at color carefully, in various kinds of lights. Gemstones will most likely look different under lamp light than sunlight.
The color distribution of rough gemstones
Rough gemstones and minerals usually display uneven color distribution that can be caused by different aspects, such as:
- Color zoning
- Sectoral color distribution
- Irradiation Factor
Color zoning of rough gemstones
Chemical and physical changes in the environment during crystal growth can cause variations of color. The most common cause is variation in the chromophore elements that causes the more or less intense color in different growth zones of the same crystal.
In some rough gemstones, color zoning corresponds to different saturation of the same color. Color zones can be easily seen by the naked eye or visible only under the microscope, color zoning can be wide or narrow. They can be uniformly formed in all directions or have very different thicknesses depending on crystallographic orientation, as a result of unequal growth velocity on different crystal faces.
Commonly the uneven color distribution deeply affects crystal value or quality factors and cutters try to avoid color zoning visible from the crown.
However, for some gems i.e tourmaline, color zoning can become very profitable when two or more different colors are clearly visible.
The sectoral color distribution of rough gems
During the initial stages of crystal formation, the growth sector can be described as a pyramid with the base corresponding to the crystal face and the apex in the center of the crystal. However, in most circumstances, the shapes of growth sectors are more complicated, due to changes in crystal habit
Different growing levels in crystal structure have different capacities to consolidate impurities
As a result, growth sectors formed by crystals usually have slightly different chemical composition, which will also cause variations of physical properties i.e color, refractive indexes
The sectorial color distribution is a common phenomenon in many gems
It is also responsible for a special gem variety such as ametrine, where same quartz amethyst and citrine coloration is observed in different growth sectors
Curiously, synthetic ametrine has color zoning as a mechanism for the formation of two different colors within the same crystal
Irradiation Factor of gemstones
Irradiation is also one of the most traditional treatments for gemstones, applied to a wide variety of gems to produce or intensify their color
Natural irradiation in many instances causes non-homogeneous coloration because certain parts of the crystal may stay in closer vicinity to the source of irradiation
Such are the cases of green sports on some diamond crystal or black halos around uranium and thorium minerals included inside quartz crystals
Various types of ionizing radiation can provoke the creation of optically active centers in minerals changing their color
Radioactive decay in mineral deposits is the reason for naturally occurring blue topaz, green diamonds, smoky quartzes, etc.
The penetration potential of different types of radiation is very dynamic i.e Gamma rays and neutrons passes effortlessly through large crystals and provide homogeneous color distribution
Beta rays only penetrate to a very small depth in minerals when they are used for diamond treatment, produced color concentrates in a very thin layer close to the surface, usually on the pavilion
Lastly, alpha rays have very low penetration power and are not suitable for gem treatment
The shape of faceting rough gemstones:
Generally, you want a faceting rough gemstone that’s “rounded” or “blocky”
Flat or twisted shapes rough gemstones with deep pits or valleys will yield very poorly
Here’s an example of a badly-shaped facet rough: //pic
Size of rough gems:
Everyone has there own thoughts about the rough gem size. Facet rough gemstones traders will often say you’ll get a 1-carat gemstone from a 2-carat rough gemstone. Moreover, some cutters will claim such feats regularly, but any cutter who keeps records of actual weights knows the truth.
The industry standard for commercial rough cutting is a 20% yield meaning 80% loss of weight is normal
Keeping this in mind you won’t go too wrong. If you want a 1-carat gemstone, then buy a facet rough stone of at least 5 carats. This is fundamental in understanding what to expect from your faceting rough gemstone.
Clarity of Rough Gemstones:
You want a stone that’s flawless and “clean” of any inclusions. Flaws are cracks or open cleavages or other things that compromise not only the appearance of gemstone but also its structure. A flaw breaching the surface of a stone is very bad because it hampers light at the surface as well as internally. A perfectly clean gemstone is difficult to find and is not necessarily the target. The aim is overall presentation and beauty of a gemstone, in general, flaws and inclusions are things we like to avoid in the purchase or to remove in the cutting.