How to Recognize a Rough Gemstone

Using of a dichroscope is the easiest way to identify a rough gemstone. The dichroscope looks like a longer version of a jeweler's loupe and uses internal prisms to separate white light into its individual vibrational directions as they pass through the stone. Once the light frequencies are clearly separated, it is easy to identify the exact color signatures of gemstones.

Things You'll Need

• Rough gemstone
• Calcite dichroscope
• White light source
• Dichroscope gemstone color chart

Instructions

1. Hold the rough stone directly in front of a white light source so the light shines through it. Then touch the lens of the dichroscope to the stone. Look through the dichroscope's eyepiece.

2. Note the color or colors of the two squares seen inside the dichroscope.

3. Rotate the dichroscope slowly between your fingers while you look through the eyepiece and watch the color squares inside the instrument for a full rotation of the instrument. Note the colors of the squares. If the two color squares inside the dichroscope are always the same color, the gem is a single refractive. If the squares present two colors that are always the same then the gem is dichroic, meaning white light passing through it is fractured into two different vibrational frequencies. If a third color presents itself as the instrument is rotated, the stone is trichroic, meaning light passing through it is fractured into three different vibrational frequencies.

4. Refer to a dichroscope color chart and find the color or colors that match those observed through the instrument. The colors or color combinations are identified by gemological name and identify the precise gem.

Tips & Warnings

• Do not use fluorescent light, as it often produces false readings within the instrument.

References

• Jewel Info 4 Your: Dichroscope Gemstone Testing Tools
• Gram Faceting: What is a Dichroscope?
• B.W. Smigel: Optical Properties of Gems