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Gemstone Identification Lab

Identifying Gemstones with Raman Spectroscopy

Learning Objectives:

  1. Identify and determine authenticity gemstones using Raman spectroscopy

  2. Understand importance of differentiating between gemstones

 

Background:

Gemstones can be found in a large variety of colors, shapes, and sizes. For example, quartz, a very common crystal, has many varieties including transparent crystal; translucent amethyst (purple), citrine (yellow), milky (white), rose (pink), and smoky (gray); and opaque agate, jasper, and onyx. Due to the large variety of ways minerals can form and their similarity in appearance it is important to be able to identify and distinguish between different minerals.

 

This is especially important to properly identify gemstones when it comes to the sale of these valuable crystals. Many synthetic and colored gems are on the market. Dealers can also, by mistake or not, sell other gems that look like the desired gem. Cubic zirconia can be pawned off as diamond, colored glass as peridot, citrine quartz as topaz. Many of these can slip past the eye of an experienced collector.

 

The method of Raman spectroscopy is a definite way to determine the true composition of crystal. Each mineral has its own unique Raman “fingerprint”. Once the Raman signal of a sample is taken it can be matched with its true composition. This method works by detecting how bonds stretch in the crystals. A mineral such as diamond, which only contains carbon atoms, will only show one peak which represents the motion of the bonds between carbon atoms. Minerals with a variety of atoms will show many peaks.

When taking data with Raman it is important to get a good signal. If a signal is saturated, the instrument is not able to intake the full signal causing a flat peak at the maximum. If the signal is too weak the output will be fuzzy. The easiest way to fix this type of problem is to change in integration time which is the duration of time the laser is on.