Panning for Gemstones: The Raman Rush

Fall is a season of harvest and festivals, which makes it an ideal time to get outside while the weather cools off and try something new. In the USA, many farms are open to the public for pumpkin patches and apple picking. In addition, other fun activities like tractor rides, corn mazes, pig races, and apple canons attract people of all ages. One such activity is panning for gemstones. This activity aims to find colorful stones hidden in a pouch of sand by sieving the sand in flowing water. Participants can get a wide variety of rocks from this pouch, including valuable stones like sapphire and emeralds. However, evaluating the value of rocks without training or equipment is impossible for most. So we analyzed the large stones found in a bag of sand at one of these fall events using Raman technology, hoping to find a diamond.

The Raman spectra were collected using i-Raman Plus 785 coupled to a video microscope with a 10x objective. Lower magnification objectives generate a larger spot size laser, which helps identify heterogeneous samples. Raman spectra collected using BWSpec software was imported to BWID software for identification with the Gem library – GemExpert’s spectral library of greater than 450 spectra of 300 different gemstones. Figure 1 shows the representative spectra of the stones.

Figure 1. Raman spectra of representative stones found in a bag of gemstone sand.

Using B&W Tek’s Raman instrument and BWID software, it was possible to collect Raman spectra of all minerals found in the bag of gemstone sand. Some rocks appear to be a mixture of two minerals, like quartz and fluorite (Fig. 2) and subtle difference in Raman spectra of different colored sub-groups can be observed and analyzed (Fig. 3). Unfortunately, there were no valuable stones among the larger stones, but don’t be discouraged, you could be the lucky one to find a chunk of diamond.

Figure 2. Raman spectra of a stone which seems to be a mixture of Quartz and Fluorite.

Figure 3. Raman spectra of sub-groups of chalcedony. 

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