Colored Stones Essentials

Organic

Once living, or produced by a living organism.

Mineral

A natural, inorganic substance with a characteristic chemical composition and usually characteristic structure.

Inorganic

Composed of, or arising from, non-living matter.

Chemical Composition

Kinds and relative quantities of atoms that make up a material.

Durability

A gemstone’s ability to withstand wear, heat, and chemicals.

What are the three traits of all gems?

Beauty, rarity, and durability

Chemical Formula

Written description of a material’s chemical make-up.

Trace Elements

Atoms in a gem that aren’t part of its essential chemical composition.

Crystal Structure

Regular, repeating internal arrangement of atoms in a material.

Amorphus

Lacking a regular crystal structure.

Luster

The appearance of a material’s surface in reflected light.

Transparency

Degree to which material allows light to pass through it.

Transparent

Light passes through a material with little or no distortion.

Translucent

Light diffuses as it passes through the material.

Hardness

How well a gemstone resists scratches and abrasion.

Toughness

How well a gemstone resists breaking, chipping, and cracking.

Stability

How well a gemstone resists the effects of light, heath, and chemicals.

Gem Species

A broad gem category based on chemical composition and crystal structure.

Gem Variety

A subcategory of species, based on color, transparency, or phenomenon.

Phenomenon

An unusual optical effect displayed by a gem.

When did the US Congress create the Federal trade Commission (FTC)?

1914

When did the FTC publish Trade Practice Rules for the Jewelry Industry?

1957

What is the most important factor in a colored stone’s beauty?

Color

What three things are required for color to exist?

Interaction of light, an object, and an observer

Selective Absorption

Process by which a material absorbs some components of visible light and returns others.

Hue

The first impression of an object’s basic color.

Tone

Degree of darkness or lightness of a color.

Saturation

A color’s strength or intensity.

Bodycolor

A gemstone’s basic color, determined by its selective absorption of light.

Color Center

A small defect in the atomic structure of a material that can absorb light and give rise to a color.

Color Zoning

Areas of different color in a gem, caused by variations in growth conditions.

What kind of light looks best for green, blue, and violet gems?

Fluorescent lighting

What kind of lighting looks best for red, orange, and yellow gems?

incandescent light or the sun’s rays at sunset

Pleochroism

When a gem shows different bodycolors from different directions.

Color Range

The selection of colors in which a gemstone occurs.

Fine Color

The color or colors in a gemstone’s color range considered by the trade to be the most desireable.

Window

An area of weak saturation in a transparent gemstone’s bodycolor that usually results from the way the gem was cut.

Extinction

Dark areas in a faceted transparent colored stone.

What type of effect is shown here?

color zoning

What type of effect is shown here?

pleochroism

What cutting effect is shown here?

window

What cutting effect is shown here?

Extinction

Dispersion

The separation of white light into spectral colors.

Fluroescence

Emission of visible light by a material when it’s stimulated by ultraviolet radiation.

Trade Terms

Terms used to describe gemstone colors or link gems with specific locations.

Play-of-Color

The flashing rainbow colors in opal.

What type of phenomena is this?

Play-of-color

Adularescence

The cloudy bluish white light in a moonstone, caused by scattering of light.

What type of phenomena is this?

adularescence

Color Change

A distinct change in gem color under different types of lighting.

What type of phenomena is this?

color change

Chatoyancy

Bands of light in certain gems, caused by reflection of light from many parallel, needle-like inclusions or hollow tubes.

What type of phenomena is this?

chatoyancy

What type of phenomena is this?

milk and honey

Milk and Honey

A two-toned effect seen when a chatoyant gem is positioned at right angles to a light source.

Asterism

Crossing of chatoyant bands, creating a star in the dome of a cabochon.

What type of phenomena is this?

asterism

Labradorescence

A broad flash of color in labradorite feldspar that disappears when the gem is moved.

What type of phenomena is this?

labradorescence

Iridescence

A rainbow effect created when light is broken up into spectral hues by thin layers.

What type of phenomena is this?

iridescence

Orient

Iridescence seen in some natural and cultured pearls and mother-of-pearl.

Aventurescence

A glittery effect caused by light reflecting from small, flat inclusions within a gemstone.

What type of phenomena is this?

aventurescence