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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Shattuckite Information's

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Shattuckite Group

The Shattuckite group is a mineral group that includes Shattuckite, Plancheite, and other rare copper silicate minerals. Here's some information about the group:

  • Chemical Formula: Cu5(Si2O6)2(OH)2
  • Discovery: The Shattuckite mineral was discovered in 1915 in Bisbee, Arizona, USA by Albert F. Holden, who named it after the nearby Shattuck Mine. The Plancheite mineral was discovered in 1898 by Gustave Désiré Froment-Meurice and named after the French explorer Jules François Émile Planché.
  • Physical Properties:
    • Color: Blue, green, or blue-green
    • Crystal System: Orthorhombic
    • Hardness: 3.5-4
    • Density: 3.5-4.3 g/cm3
    • Cleavage: Perfect in one direction
  • Optical Properties:
    • Refractive Index: 1.70-1.78
    • Birefringence: 0.030-0.040
    • Pleochroism: Distinct
  • Ranking of Rarity: Shattuckite and Plancheite are both considered to be rare minerals.
  • Occurrence (Countries): Shattuckite is found in the USA, Namibia, the Democratic Republic of Congo, and Australia. Plancheite is found in the Democratic Republic of Congo, Zambia, and Namibia.
  • Healing Properties: The Shattuckite group is believed to have healing properties that can help with communication, intuition, and spiritual awareness.
  • Uses: The Shattuckite group is primarily used as a collector's mineral and in jewelry.

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