Understanding Gemological Analysis and Identification Techniques

Introduction

Welcome to our GIA Knowledge Sessions, a series of talks and seminars about gemology fueled by decades of research. At GIA, we consider ourselves fortunate to be able to study and learn from gems, and it is our mission to share our discoveries and learnings with the world. In today's session, we will take a behind-the-scenes look at the analytical equipment used at GIA for gemstone analysis and identification.

The Evolution of Gemological Laboratories

Over the years, gemological laboratories have evolved to address different questions about gemstones. Initially, the focus was on identifying gemstones, distinguishing between diamonds, zircons, and other stones. As the gem trade evolved, new questions arose, such as whether a stone is natural or lab-grown, and its origin. These questions led to the development of different analytical techniques and approaches.

The Optical Approach

When it comes to identification, gemologists often consider gemstones as optical devices. By studying their refraction, birefringence, and spectrum, gemologists can determine the type of gemstone. Techniques such as refractometry, spectrometry, and polariscopy are used to analyze gemstones' optical properties.

The Geological Approach

As gemological laboratories began to encounter lab-grown stones and treated gemstones, a geological approach was adopted. This involved understanding how gemstones are formed within the Earth. By examining the inclusions and mineral composition of gemstones using a gemological microscope, researchers can determine whether a stone is natural or lab-grown and identify any treatments it has undergone.

The Mineralogical Approach

For more complex questions, such as origin determination, a mineralogical approach is taken. This involves analyzing the trace element chemistry of gemstones using techniques like laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). By measuring the concentration of elements and comparing it to known reference materials, gemologists can determine the origin of a gemstone.

Analytical Techniques

Classical Techniques

Classical gemological techniques involve standard gemological testing and microscopic observations. Refractometers, polariscopes, and spectrasopes are used to determine a gemstone's optical properties, such as refractive index and optic sign. Microscopic observations, using a gemological microscope, allow gemologists to examine the inclusions and growth patterns of gemstones.

Advanced Techniques

Advanced analytical techniques, such as spectroscopy and trace element chemistry, provide more detailed information about gemstones.

Spectroscopy

Spectroscopy involves measuring how gemstones interact with electromagnetic radiation. Techniques like UV-Visible Spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR) can be used to identify the presence of specific elements or treatments in gemstones. For example, UV-Visible Spectroscopy can help identify lead glass-filled rubies by detecting characteristic lead peaks in the spectrum.

Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS)

LA-ICP-MS is a powerful technique that allows for the measurement of trace element chemistry in gemstones. By ablating a small amount of material from a gemstone and analyzing it using mass spectrometry, gemologists can determine the concentration of elements and make origin determinations.

Raman Spectroscopy

Raman spectroscopy involves shining laser light on a gemstone and analyzing the scattered light to obtain information about the gemstone's molecular composition. It can be used to identify different minerals present in gemstones and detect treatments or synthetic materials.

Conclusion

Gemological laboratories employ a range of analytical techniques to study gemstones and provide accurate identification and origin determinations. From classical gemological testing to advanced spectroscopic and chemical analyses, these techniques help gemologists better understand gemstones' properties and characteristics. By combining these techniques, gemologists can confidently identify gemstones, detect treatments, and determine their origins.

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