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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Azurite Mineral History , Properties and Uses

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Azurite Mineral

History

Azurite is a copper carbonate mineral that has been known since ancient times. The name "azurite" comes from the Persian word "lazhward", which means blue. It was used in ancient Egypt and Greece as a pigment for painting and in jewelry making. Azurite was also used by the ancient Chinese and Native Americans for ornamental and medicinal purposes.

Discovery

Azurite is found in copper deposits worldwide, especially in areas with arid climates like Arizona, New Mexico, and Utah in the United States. It is often found in association with malachite, another copper carbonate mineral. Azurite was first described scientifically in 1824 by the French mineralogist François Sulpice Beudant.

Chemical formula & Physical Properties

Chemical FormulaCu3(CO3)2(OH)2
ColorAzure blue
Crystal SystemMonoclinic
Hardness3.5 - 4
LusterVitreous
StreakLight blue

Optical Properties

Azurite is a pleochroic mineral, which means that it shows different colors when viewed from different directions. It has a refractive index of 1.730 - 1.838 and a birefringence of 0.108 - 0.146. Azurite is also fluorescent under shortwave ultraviolet light, appearing bright green.

Uses

Azurite is a popular mineral for collectors and lapidaries due to its beautiful blue color and interesting crystal formations. It is also used as a pigment in painting, although it is not as stable as other blue pigments like ultramarine. Azurite is sometimes used in jewelry making, but it is not very durable due to its softness. In addition, azurite is sometimes used in alternative medicine for its supposed healing properties.

Pictures 

https://www.mindat.org/gm/447



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