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What Makes a Gem a Precious Stone
Gemstones have long been treasured for their beauty and durability.
Their value will vary based on the rarity of the stone, and the skill with which it has
been cut. A wide variety of stones have been used as gems, and over the years some
types of stones have become worthless, and others have become priceless. To the ancient
inhabitants of many regions, pretty stones served as the first currency. Residents of
some pacific islands used carved stones weighing several tons as their method of
measuring wealth. Throughout recorded history, the smaller stones we think of as gems
have been used as a way to hold or safeguard wealth. Second only to the precious metals,
investment in gemstones has been most widely used as a means of protecting one's wealth in
times of war or in exchanging value in distant lands.
Tsavorite Garnet courtesy of theimage.com
The beauty of gemstones depends on the optical properties
that the stone possesses and the skill of the craftsman who cut and polished it.
Some of the optical properties can be measured, while others are more subjective
and can be described only with imprecise terms. The stone's color and refractive
index are the two most widely used measurable optical properties. Other measurable
properties include dichroism, dispersion and absorption. Asterism is an effect that
is sometimes displayed, but not measured. Other unmeasured properties include
play of color, chatoyancy, and luster.
Rhodalite Garnet courtesy of theimage.com
Refraction is a measure of how light is 'bent' within a
stone. Dichroism is used to describe a gem's tendency to display different colors
from different angles. Dispersion and absorption measure the amount of
light in a given spectrum that is absorbed or dispersed. Asterism and chatoyancy
are similar in that they produce concentrated bands of light such as in tiger-eyes
or stars. Luster is a description of how shiny the stone is.
The cut of a gemstone adds greatly to its beauty. Many
gems found in nature are unrecognized by the average person until the craftsmen
that cut and polish the stone release the beauty of the gem. Although the cutting
of a stone may at first seem a simple thing - make a flat top that tapers to a
point at the back - cutting is actually a precise, mathematical operation. The
angle of the facets are calculated to bring the most 'fire' and beauty to the gem,
while not cutting in ways that would weaken the stone. Many stones must be cut at
certain angles in relation to the natural planes within the stone to prevent the
stone from 'cleaving' or breaking.
Tourmaline courtesy of theimage.com
A gemstone's value is based on the stone's type, size
and quality. The rarity of a stone-type will vary based on its size. Small
tsavorite garnets, which are widely available, are relatively inexpensive, but
large ones are very rare and much more expensive per carat. Quality will also
have a major impact, often the price will double from a low grade stone to a high
quality gem of the same type. Current political, economic, and military conditions
within the region that produces the gem may affect the prices paid as well.
Zircon courtesy of theimage.com
Copyright © 2005 by Gem And Mineral Info.com.
All descriptions and images, except where noted, are the property of
Gem And Mineral Info.com
Where noted images and descriptions are used with permission of copyright
holder as indicated.