How to Identify Crystals & Semi-Precious Gemstones

Written by darcy sautelet
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Rocks are one of the most amazing historical representations of our planet. Some rocks are valuable, such as lapis lazuli, amber and jet. But it is actually pieces of mineral that become attractive when polished or cut that are considered "semiprecious" or "precious" gemstones. Quartz crystal, one of the most common minerals on our planet, is attractive even in its natural form. Rocks and minerals share two characteristics: They are both formed naturally by the earth, and they are both solid. Minerals, though, have a defined chemical make-up and a crystal structure. Distinguishing a crystal or semiprecious gemstone from a rock is sometimes a daunting goal for the rock and gemstone hobbyist. There are methods to determine if your stone should at least be looked at by a competent gemologist.

Skill level:

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Things you need

  • Hand lens (pocket magnifier)
  • Field Guide for Rocks & Minerals
  • Rock & Mineral Test Kit ($9.00)
  • Streak Chart
  • Small LED light
  • Water

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  1. 1

    Wash the stone and let it dry. If it is rough, sandy or extremely soft, it is most likely not a gemstone. Now observe the colour. Color is one of the first steps in identifying semiprecious stones, but identification can not be concluded from colour alone.

  2. 2

    Observe the structure with your hand lens and then compare to samples in your field guide. There are six basic crystal systems: isometric, tetragonal, hexagonal, orthorhombic, monoclinic, and triclinic. Determine which crystal system your stone has.

  3. 3

    Test the "streaking" of your stone, using the white, unglazed piece of tile in your test kit. If you don't have a test kit, any unglazed white tile will work. Compare the streak to your streak chart to help identify which mineral you may have.

  4. 4

    Decide the hardness of the stone, using your test kit. Minerals are rated on the numerical Mohs Scale from 1 (softest) to 10 (hardest). Each mineral can scratch a stone with its own hardness or lower. Using the stones provided in your kit, eliminate by starting at the sample 10 then working your way down the scale until the stone scratches the sample.

  5. 5

    Observe your stone's lustre and transparency using your LED light. Use your light to determine the transparency and the "fire" inside the stone, estimating its intensity as weak, moderate, strong or extreme.

  6. 6

    Separate and label stones according to your observations. It is helpful to make notes on each step. Most local rock shops will look at your stones for free so take them in to verify your findings.

Tips and warnings

  • --The field guide is a collector's best friend. With diagrams, clear photographs, and information on a multitude of minerals, the guide is one item you should keep in your bag.
  • --Gemstones are usually cold to the touch. Put the stone to your lips and see if it is cold. (A diamond will stay cold even in your mouth)
  • --Many areas in Colorado, Utah, South Dakota, and Montana are rich in semiprecious gemstones. Creek beds hold not only gold and silver but also semiprecious and even precious gemstones.
  • -- Do not trust your observations only. If you have any doubt, take your stone to a qualified gemologist to determine its identity.

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