Gemstones, Diamonds, Pearls -
My Shopping Cart My Account Gem Library
|Welcome to|Single Stones|Calibrated Stones|Pairs|Mix Lots|Closeouts|Carved Gems|lapidary and gemological tools and supplies|Gem Smart Search|
 Home / Gem Library / Resources / Optical Properties June 25, 2024  

Optical Properties of Gemstones

Colour is the most important factor in determining the value of gemstones and its the most obvious visual feature, but in fact it is just one of many optical properties, all of which are dependent upon light.

Luminescence incorporates a gemstone’s ability to emit visible light in darkness when exposed to ultraviolet light (fluorescence, named after flourite, the predominant flourescent gemstone), and in the case of kunzite, to produce an "afterglow" which lingers after the light has ceased (phosphorescence).

The luster or brilliance of transparent gems is caused by light reflecting from the stone's surface. The smoother and more highly polished the surface is, the greater the luster will be. High light refractivity of a gem will cause greater luster as well. The most intensive luster is seen in the highest refractive indices, diamond, zircon, and rutile, and is known as an adamantine luster. Hematite produces a metallic luster, even though it is not transparent. Most gemstones have a vitreous or glassy luster, but there are other types of lusters, including resinous (amber), greasy (serpentine), waxy (turquoise), pearly (rhodonite), and silky (tiger's eye).

Refraction is the bouncing around of light from the greater part of the light ray which hits the gemstone and passes into the stone. As it enters the denser medium of the gem, the light bends and the amount of bending or light refraction produces a measurable index (refractive index), which is often used to help identify a gemstone. When light hitting a gemstone splits into two rays traveling through the stone at different speeds and in different directions, the reaction is called birefringence or double refraction. This is seen uncommonly and in a variety of calcite called Iceland Spar as well as zircon, rutile, and sphene.

Dispersion is the separation of light into its separate spectral colors. Gemstones with the highest light refraction typically show the highest dispersion rate as well (rutile, sphene, diamond, zircon). This color dispersion or fire can be enhanced by a gem cutter if he uses an appropriate facetting style.

Color changes which are evident when viewed from different angles in gemstones (iolite, alexandrite, andalusite) is called pleochroism. It is very important for the gem cutter to cut a pleochroic stone properly in order to show off the different colors. Ruby and sapphire have two color shades and are pleochroic; in ruby, for example, yellow-red and purplish-red, which distinguishes it from garnet and red spinel, which have no pleochroicism. Iolite displays lavender-blue, gray, and pale yellow when viewed from different angles.

Knowledge Search/
Enter Keywords:
Enter one or more keywords (i.e madagascar sapphires ).

About Gemstones /

Gem Library/
Gems Legend and  Lore Gems Legend and Lore
Some of the latest of ways that gems have been associated with Birthstones and Signs of the Zodiac.
Understanding Gemstones Understanding Gemstones
Learn about Physical and Optical properties, color, clarity and cut of gemstones.
Gems Glossary Gems Glossary
Ever wonder what are "Blemish", "Luster", "Saturation" "Uniformity" or "Mine Run" means?
Reference and  Links Reference and Links
Recommended books and links to Gem, Jewelry&Mineral Magazines, Gem Institutes and Labs.

Book’s Corner/
Buy at DK Handbooks: Gemstones by Cally Hall and Harry Taylor
Price: USD 15.16
"Very good reference book to gems, stones and bones used in jewelry and ornamentations. Easy to use and read..."
see more recommendations

 Top of Page Need help?  

Gemstones for sale: Alexandrite, Garnet, Diamond, Opal, Spinel, Sapphire, Tourmaline, Tanzanite, Tsavorite,
Gemstones by Category: Calibrated, Carving, Closeout, Jewelry, Mixed Lot, Pair, Rough, Single, Best Sellers or Featured Gemstones.
Gemstone education: Colored Gemstones Guide, Gems Library, Gemstone Treatments, Gemstone Glossary, Gems and Astrology,

All Transactions secure by Thawte certificate - click here to validate Ebay Power Seller Gem Certification Various Shipping Options Major Credit Cards Accepted

All trademarks and logos shown herein are the property of their respective owners. © Copyright, 1998-2011. All rights reserved. Use of this site constitutes acceptance of Return Policy, Privacy Policy and Trading Guarantee. Published and operated by David Wein Ltd. 32 Hollywood Road, Central, Hong Kong Island Hong Kong. Lost? Check site map or resources page.

Site design and maintenance by NetComposite ®.