Gemstone Windows and Dark Patches: What to Look for in a Cut Gem

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AI-generated educational illustration. Conceptual only; not a photograph of an actual specimen or location. A coloured gem may have a pale, see-through centre or areas that look almost black. Both affect its appearance, but they do not have the same cause. What is a window? A window is an area where light passes through the gem instead of being returned towards the viewer. You may see the background through it, especially near the centre. Cutting angles and the material's refractive index—how it bends light—help determine whether this happens. There is no single ideal depth for every gemstone. Why dark patches need a closer look Darkness can have several causes. The material may absorb a lot of light. Some facets may reflect dark surroundings or the observer. Extinction is another cause, involving light that is not returned to the viewer after internal reflection. For that reason, calling every black patch “extinction” can be misleading. A simple viewing routine Look at the gem fac...
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Dyed Rock Crystal (Quartz) sold as a Pink Topaz

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"Cover the sun with a finger"

"Recently, the CIGTL-Gemological Laboratory of Pakistan received two mineral specimens with a pink crystals.

Dyed quartz examined in the pink-topaz imitation case study

Both mineral specimens were submitted to confirm the pink crystals, whether they are pink topaz or something else.

Dyed quartz examined in the pink-topaz imitation case study

Upon initial observation, it becomes readily apparent that the presence of pink crystals within the host rock is a direct result of human intervention.

Dyed quartz examined in the pink-topaz imitation case study


Upon closer examination of its crystalline structure and horizontal growth striations, it becomes evident that both pink crystals are, in fact, rock crystals (colorless quartz) embedded in rock using binding material.
The pink hues are due to a layer of paint applied to the backside of the crystals.


Dyed quartz examined in the pink-topaz imitation case study


Location: J7Q9+HJ Dianbai District, Maoming, Guangdong Province, China

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