Learn about gemstone color, crystallography, hardness, chemical makeup and more.

Gemstone Color Measurements and Specifications

Gemstone color measurements are hard to make with conventional color-order systems. Learn how recent colorimetry tech advances have improved accuracy.

crystallography - bladed baryte
Descriptive Crystallography for Gemologists

Gemologists deal with many crystalline minerals. Learn the most common terms used in crystallography to describe their appearance and structure.

gem color - GIA hues
Evaluating Gem Color: Hue, Tone, and Saturation

Accurately describing gem color is critical to determining a gemstone's value. Learn how to grade hue, tone, and saturation and avoid some common pitfalls.

malachite - idiochromatic gems
What are Allochromatic and Idiochromatic Gems?

Learn the difference between allochromatic and idiochromatic gems and why some gem species can occur in many color varieties and others occur only in one.

Gemstone magnetism - ruby and spinel
Gemstone Magnetism: The Forgotten Property

Although gemstone magnetism isn't commonly tested, it can help gemologists distinguish similar looking gems. Learn how to analyze this property.

Optics in Gemology

The optical properties of gemstones and minerals are determined by their crystallographic symmetry. Learn more about optics and gem identification here!

iris agate - phenomenal gems
Phenomenal Gems - Unique Phenomena in Gemstones

Phenomenal gems seem to do magical things with light. Learn the optical effects behind these displays and how to judge the value of these beautiful stones.

gemstone thermal properties - marble
Gemstone Thermal Properties

Non-destructive tests are critical for gemologists trying to identify gems. Learn how measuring thermal properties, especially thermal inertia, can help.

gemstone enhancements - irradiated topaz
What are Gemstone Enhancements?

Gemstone enhancements improve the appearance and wearability of gems. Learn about the most commonly used procedures and frequently treated types of gems.

Understanding Color in Gemology

The color of a mineral or gemstone is one of the primary attributes used for identification,but it is, unfortunately, one of the least diagnostic and useful

gemstone luminescence
What is Gemstone Luminescence?

Gemstone luminescence is a glow that occurs when certain stones are subjected to energy such as UV light. This effect can help gemologists identify gems.

Fluorite - gemstone cleavage
What is Gemstone Cleavage?

Gemstone cleavage is a break in a crystal along internal planes. Learn the science behind this and the difference between cleavage, fracture, and parting.

gemstone optical properties - hambergite
Gemstone Optical Properties

Learn how gemstone optical properties, like refractive index and pleochroism, help gemologists with identifications and lapidaries choose gem cuts.

What Is Gemstone Pleochroism?

Learn why some gems reflect multiple colors (pleochroism) and how gemologists use colors to identify gemstones.

Trapiche Emerald

Trapiche emeralds are formed when black carbon impurities fill in the emerald crystal junction which forms a radial pattern with a six-pointed star effect.

gemstone color change - stillwellite
Gemstone Color Change Phenomena

Why do certain gems change color under different lights? Explore gemstone color change phenomena and the difference between natural and artificial light.