What is gemology?
Gemology is the study of the physical and optical properties of gem-quality crystals, or colored gems.
Gems come in a wide varieties and colors, and the gemologist acts as a detective to determine the nature of the stone—that is, whether it is natural, treated, synthetic, or an imitation.
Presentation of gemological instruments
A 10x magnifying glass: after the eye, the essential tool for observation.
A carat scale: one carat = 0.20 grams.
A lamp adjusted for dark-field illumination, lighting the stone from behind, allows close observation of inclusions and certain treatments.
A refractometer measures the speed and angle of incidence of light traveling through a stone, thus determining its refractive index. Each type of stone has a specific refractive index and a diagnostic birefringence (or lack thereof).
A polariscope is used to determine the crystalline nature of the material (isotropic or anisotropic). Crystallographic analysis also helps determine these properties.
A dichroscope for observing the pleochroism of anisotropic materials.
A Chelsea filter for determining the presence of chromium. Notably used for identifying emeralds.
A spectroscope allows the reading of absorption spectra on a band representing the visible light spectrum. These instruments can diagnostically determine the presence of chemical elements composing a gemstone, influencing its color, for example.
Not shown in the photo: a UV lamp, a very useful instrument for completing the analysis and observing the reactions.
What is microphotography?
Microphotography involves studying and photographing the inclusions in a gemstone using a microscope equipped with a camera. Magnification can reach 100x. These inclusions serve as essential diagnostic markers for gemologists to determine a stone's identity. They can also reveal traces of treatments and optical phenomena, making them an indispensable tool for gem identification and study.
Here are some photomicrographs taken with the Motic GM171 microscope:
