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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Build Your Gemology Knowledge with 529 Practice Questions

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Interested in gemstones and the science behind them? Gemology MCQs: Gemstones Study Guide offers a structured way to learn and review key gemology concepts through multiple-choice practice.

The first edition includes 529 questions across 108 topics in a 177-page PDF, designed for beginner to intermediate learners. Questions cover gemstone formation, physical and optical properties, crystal shapes, inclusions, faceting, synthetic gems, imitations, enhancement, and identification.

You’ll also find quizzes on many individual gemstones and varieties, including diamond, garnet, beryl, quartz, chalcedony, corundum, and tourmaline. A dedicated 50-question section on physical properties reviews topics such as hardness, cleavage, fracture, specific gravity, and carat weight.

Answers and explanations support self-paced review. When a source question does not include a separate explanation, the guide identifies that clearly.

Get the study guide

The ebook is available as a digital PDF. View the product page and get your copy here:

Square navy-and-gold cover for Gemology MCQs: Gemstones Study Guide, featuring a collage of colorful gemstones and the text “529 Questions | 108 Topic Quizzes.”
Gemology MCQs eBook


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