COLOR KEY-its role in finding a real gem.

When identifying a gemstone, a gemologist will want to hold it, feel it, and examine it from all angles. This is done to assess the appearance of the stone: the luster, the color, and any other features. A hand-held lope may be used to search for scratches and flaws on the surface which may give an indication of hardness, while a scratch inside the stone may reveal characteristic inclusions. These features may be unique to one gem, but further tests may be necessary to identify synthetic or imitation stones. From this initial examination, however, the gemologist should know which tests to perform.

HOW THE COLOR KEY WORKS:

This key puts all gems into one of seven color categories, though color varieties within some species may appear is more than one. Each color category is divided into three sections: gems that are always that color, gems usually that color, and gems sometimes that color.

Many gems appear the same color, but can be distinguished when viewed with a spectroscopy. This reveals an absorption spectrum that is unique to each gemstone.

OPTICAL PROPERTIES

Color is the most obvious visual feature of a gem, but infect it is just one of ,many optical properties, all of which are dependent upon light .The individual crystalline structure of gemstone ,interacts with light in a unique way ,and determines the optical properties of each gem species.

WHAT MAKES COLOR?

The color of a gem depends largely on the way it absorbs light. White light is made up of the colors of rainbow, and it strikes a gem some spectral colors are “preferentially absorbed”. Those that are not absorbed, pass through or are reflected back, giving the gen its color. Each gem infect has a unique color “Fingerprint”

ALLOCHROMATIC GEMS:

Allochromatic (“other-colored”) gems are colored by trace elements or other impurities that are not an essential part of their chemical composition. Corundum, for Example, is colorless when pure but impurities in it create the red stone we know as rubies, blue, green and yellow sapphires and orange-pink padparadscha. Allochromatic gems are often susceptible to color enhancement or change.

IDIOCHROMATIC GEMS:

The color of idiochromatic (“self-colored”) gems comes from elements that are an essential part of their chemical composition. Thus idiochronatic gems only have one color. Peridot, for example, is always green, because the color is derived from one of its essential constituents, iron.

PARTI-COLOURED GEMS:

A crystal that consists of different-colored parts is called parti-colored. It may be made up of two colors, three, or more. The color may be distributed unevenly within the crystal, or in zones associated with growth. The many different varieties of tourmaline probably show the best example of parti-coloring, exhibiting as many as different colors or shade within a single crystal.

PLEOCHROIC GEMS:

Gems that appear one color from one direction, but exhibit one or more other shades or colors when viewed from different directions, are known as plethoric. Amorphous or cubic stone show one color only; tetragonal, hexagonal or trigonal stones show two colors; orthorhombic , monoclinic ,or triclinic stones may show here colors.