How to Test for Copper in Tourmaline

Written by sean lancaster
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How to Test for Copper in Tourmaline
Discover which metal ions give your gems colour. (garnet gemstones image by Julianna Olah from Fotolia.com)

Tourmaline is a group of gemstones that vary in colour based on the metal ions incorporated into their crystalline lattice structure. The proper name for the class is Elbaite. The gemstone is a complex sodium aluminium borosilicate bearing lithium. The colour of tourmalines ranges from pinks to greens. Cuprian Elbaite refers to tourmalines that have copper as the principle colour-producing metal. The colour of these tourmalines ranges from deep green to purples. Other metal ions may be present and add their own colour to the appearance but copper is one of the most common.

Skill level:
Moderate

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Things you need

  • Spectrophotometer

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Instructions

  1. 1

    Obtain the absorption spectrum of the tourmaline using the spectrophotometer. The first indicator of the presence of copper is to look for the characteristic absorption band at 695 nm. This doesn't conclusively indicate that copper is present.

  2. 2

    Send a sample to an analytical laboratory to perform two tests that will determine which metal ions are present. The two tests to order are ion beam analyzer (IBA) and energy dispersive X-ray fluorescence (EDXRF). Both of these tests are non-destructive and can check for the metal ions present in the sample.

  3. 3

    Contract an analytical laboratory to perform laser ablation inductively coupled plasma mass spectrometry analysis on your sample. This is the most recent analytical technique that applies to the determination of metal ion content in tourmalines. This technique is essentially non-destructive due to the fact that it only requires a very minute sample.

Tips and warnings

  • Visual observation is the best screener for tourmalines that are possibly copper containing.
  • Be aware of the high cost of many of the tests run by analytical laboratories.

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