COLOR IN GEMSTONES
Many gems appear colored because part of the white light traveling through them is absorbed within the mineral structure. White light is
a mixture of many colors but only when one or more of these colors is removed does the light emerging from a gem appear colored. Like everything
else we see, gems absorb and return light. But each gem species and variety contains a unique mix of chemicals. And each gem crystal grows in
it's own way. A gem’s chemical composition and its crystal structure combine to affect the way each gem absorbs and returns light. Like the
ingredients in a recipe, these natural variations contribute to each gem’s unique body color.
Many gemstones have unique characteristics in appearance due to irregularities in crystal structure, light absorption, and inclusions.
Color zoning or banding
Some gemstones such as amethyst will display bands of lighter and darker color. This is a natural occurrence due to changing conditions during the crystallization process.
Pleochrosim
Pleochroic gems display different body colors depending on your viewing direction. Tanzanite is one of the most popular pleochroic gems, showing violet-blue from some directions and mostly purple in others.
Color-change
A chameleon-like quality that few gems possess. Depending on the light the gem is exposed to, the color of the stone will change. This is most often noticed in the gemstone Alexandrite, which often changes from a purplish red to a bluish green.
Asterism
When needle like inclusions diagonally cross the center and highest part of a gemstone, they usually create a four or six rayed star. This is most common in the Star Ruby and Sapphire.
CLARITY
A major part of any transparent stone’s value is its clarity, which is its degree of freedom from blemishes or inclusions. Colored stones have
many different kinds of blemishes and inclusions, with many different effects on a gem’s appearance and durability. Some inclusions make a positive
contribution to beauty and value.
Outside of clarity’s relationship with appearance and durability, there’s also a close relationship between clarity and rarity. Because of the
way gems form, the chances of a truly inclusion-free gem are extremely remote. The fewer inclusions a gem has, the rarer it is. And, as you might
guess, this rarity also makes it a lot more valuable, all other factors being equal.
CUT
Cut is the human contribution to a gemstone’s appearance. The ability of the stone cutter is essential to how well the gemstone returns light
and displays color. After color, the shape (the stone’s face up outline), is usually the first thing you notice about a finished colored stone. The
round is the most familiar shape. All others are generally classified as fancy shapes. These include oval, emerald, pear, marquise, trillion,
cushion, princess, and heart. The cabochon cut is a smoothly domed top with a flat bottom, used mostly on gemstones such as opals.
DURABILITY
A gemstone’s durability is a combination of three factors: hardness, toughness, and stability. Hardness measures how well a gemstone resists
scratching. Hardness is measured by the MOHS’ scale. The scale consists of a series of ten specified minerals in order of their relative
hardness (the tenth being the hardest.) The MOHS’ scale can be confusing. Keep in mind that the increments of hardness between the listed
minerals are not equal or proportionate. For example, the difference in hardness between 9 (Corundum) and 10 (Diamond) is much greater than
between 8 and 9. Toughness is the ability to withstand breaking and chipping within the gemstone and stability measures how well a gemstone
resists the effects of light, heat, and chemicals.
|