Rough Gemstones, Raw Stones or Uncut Gemstones
Rough Gemstones, also referred to as raw stones or uncut gemstones, are earth-mined stones in their unprocessed state. These natural gemstones are extracted from the earth at different locations worldwide, untouched by cutting or polishing, allowing their innate beauty and elemental energy to remain intact. These raw stones are used for,
- Jewellery Creation: Transforming raw gemstones into exquisite jewelry pieces.
- Decorative Art: Enhancing interiors with the natural charm of uncut stones.
- Healing and Meditation: Uncut stones are a powerful source of energy, as mentioned by healing crystal healers.
- Collectors’ Items: Rare specimens of rough stones are preserved for their raw beauty as part of a gemstone collection.
How to Evaluate Rough Gemstones?
To evaluate the value of rough gemstones, it requires attention to four key factors. These factors are color, shape, size, and clarity. Apart from these factors, origin (the place where the rough gemstone is mined) also plays a great role in evaluation. For example, a Burma Sapphire rough is valued much more in comparison to Madagascar Sapphire rough, assuming all other factors are the same.
Color
The color of a gemstone plays the most critical role in its value. According to the Gemological Institute of America (GIA), color quality accounts for over 60% of a gemstone’s worth. Always look for:
- Even Color Distribution: While some rough gemstones exhibit color zoning (irregular distribution of color), an evenly saturated hue often enhances value.
- Lighting Impact: Examine stones under different lighting conditions, as they may appear different in natural sunlight compared to artificial light. Normally, rough gemstone color is best seen when they are wet, i.e., taken out of water.
Shape
Rough gemstones with blocky or rounded shapes are ideal for cutting and faceting. Avoid stones with bottomless pits, valleys, or irregular forms, as they may yield poorly during cutting.
Size
The size of raw stones significantly impacts their usability. The bigger the size, the better it is, as big pieces can be extracted from the rough. As a general rule:
- Expect about 20% yield after cutting (e.g., a 5-carat rough stone typically produces a 1-carat finished gem).
- Larger stones provide more flexibility for creative cutting.
Clarity
Clarity refers to the presence of inclusions or flaws within a gemstone. Look for stones with minimal inclusions to maximize both beauty and durability. Surface-reaching flaws may impact the gem’s structural integrity.
The Science of Color in Rough Gemstones
Color Zoning
Color zoning occurs when variations in chromophore elements during crystal formation lead to uneven color distribution. While it may affect value, some gems—like Tourmaline—benefit from visible color zones, creating bi-color or tri-color effects.
Understanding Color Zoning in Rough Gemstones
Color zoning in rough gemstones occurs when variations in color appear as the crystal grows. This happens due to chemical and physical changes affecting the gemstone’s chromophore elements (the minerals responsible for color). These changes can lead to more intense or lighter color areas within the exact gemstone.
In some rough gemstones, color zoning is visible as different saturation levels of the same color. These zones can be observed with the naked eye or only under a microscope and may appear as narrow or wide bands. Depending on the gemstone’s crystallographic orientation, the color zones may be uniformly distributed or vary in thickness.
While color zoning can sometimes lower the value of a gemstone, especially if visible from the crown, it can also add unique beauty to specific stones. For example, in gemstones like tourmaline, multiple colors within the stone are often a sought-after feature. Color zoning enhances their desirability for such gems, making them highly valuable.
Sectoral Color Distribution in Rough Gemstones
During the early stages of crystal formation, gemstones develop in specific “growth sectors” that resemble pyramid-like shapes, with the base corresponding to the crystal faces and the apex at the centre. These growth sectors often appear more complex due to variations in the crystal’s habit and the conditions during growth.
Each growth sector may have a slightly different chemical composition, resulting in variations in color and other physical properties like a refractive index. This phenomenon is common in many gemstones and can create exciting effects, mainly when the color is distributed in distinct sectors within the crystal.
One well-known example of sectoral color distribution is ametrine. This gemstone naturally combines the purple of amethyst and the yellow of citrine within the same crystal. The color zoning in ametrine occurs because different sectors of the quartz crystal form with varying chemical compositions, resulting in the distinct colors that make this gem so unique. Synthetic ametrine also features color zoning, showing how this process can be replicated in laboratory-grown stones.
The Role of Irradiation in Gemstone Color
Irradiation is a well-established treatment used to alter or intensify the color of many gemstones. This process involves exposing stones to natural or artificial radiation, which can cause non-homogeneous colouration within the crystal. Some areas of the gemstone may receive more radiation exposure, leading to different colors across the crystal.
Natural irradiation is responsible for creating specific gemstone colors, such as the green hues in green diamonds or the smoky appearance of quartz. It occurs when minerals in the Earth are exposed to natural radioactive decay, which triggers the formation of optically active centres that change the color of the stone.
The type of radiation used during the treatment significantly affects how the gemstone’s colour develops. For example:
- Gamma rays and neutrons penetrate deep into the crystal, resulting in a more uniform color distribution.
- Beta rays only penetrate gemstones’ surface layers, which is why this type of irradiation is used to treat diamonds to produce color that is concentrated near the surface.
- Alpha rays have low penetration power and are not commonly used for gemstone treatments.
In some cases, radiation can produce eye-catching color effects, enhancing the beauty and value of gemstones like topaz and quartz.
Why Rough Gemstones Are a Collector’s Delight
For gemstone enthusiasts, rough gemstones offer a window into Earth’s geological history. Each piece is unique, showcasing natural growth patterns, colors, and textures. They are an exceptional addition to any collection, capturing the raw essence of nature’s creations.
Buy Rough Gemstones at the Best Prices
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