One of the great challenges of gemology is the development of an accurate, simple, consistent, and reproducible technique for gemstone color measurements and specifications. Until the mid-80s little progress was made, despite the appearance and…

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

Step 4: Gem Grading Lesson 7 Back to syllabus What color is this? If you answered red, you are wrong. It is orange. Most people think of this color below as orange. Properly speaking, it is yellow orange. Hence the…

Gemstone color owes a little to pigments and a lot to light. Some gems get their color the same way paints receive their color.  For example, if you wanted some blue paint for your bedroom, the store clerk would take white paint and add a few drops…

Step 3: Practical Gemology Lesson 18 Back to syllabus Some time ago, I became interested in gemstone magnetism. While researching this property, I found that some gemology schools had little to say on the subject. (Many gemology…

Optical properties of gems are incredibly important in gemstone differentiation and identification. Because the optical properties of a crystal are sensitive to minute changes in composition and strain within the crystalline structure, they are…

Step 5: Advanced Gem Information Lesson 3 Back to syllabus What Are Phenomenal Gems? Some optical effects in gemstones, such as color, brilliance, dispersion, and birefringence, can be quite impressive. However, not all optical…

Gemologists are severely handicapped in analyzing and identifying gemstones because their testing methods must be nondestructive. This limits the measuring process to the areas of optics, including spectroscopy, luminescence, and so forth;…

Step 2: Advanced Gemology Lesson 5 Back to syllabus Gemstone enhancements are procedures applied to gems to improve their appearance and wearability. There are many kinds of treatments. Some have been used for centuries, while…

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 (except in a handful of cases). The colors reported include all those mentioned in the…

If you’ve ever seen a gem that appeared to be glowing, you’ve witnessed gemstone luminescence. This phenomenon occurs when electrons in certain atoms of a crystallized mineral absorb energy and then release it in small amounts over time. If the…

Just as wood is easier to split with the grain than against it, gemstone cleavage is the tendency of certain crystals to break along definite plane surfaces. If there are planes in a crystal structure with relatively weak atomic bonds, the…

The term luster is used to describe the way a mineral surface looks when light is reflecting off of it. Luster is considered a basic descriptive parameter for minerals but varies somewhat even within a single crystal, which limits the term’s…

Step 2: Advanced Gemology Lesson 1 Back to syllabus The Properties of Light Light is is such a common thing we tend to take it for granted. We have been experiencing it since birth and are very familiar with it; however, rarely do…

Gems that show two or three colors when viewed from different angles are said to be pleochroic (showing “more colors”). This quality is called pleochroism and can be found quite spectacularly in gemstones such as cordierites, andalusites, and…

What is a Trapiche Emerald? There are plenty of books and articles describing the beauty of the emerald, from its rich green tones to the jardin, (garden) inclusions that often occupy an emerald (and help to identify its origin) to its unique…

Frequently, people ask me to explain how gemstone color change works. Some stones can change color under different light sources. Although the answer is pretty complex, a few diagrams can really help.