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Mineral Identification

Minerals can be identified using properties such as color, streak, luster, density, hardness, cleavage, fracture, and others.

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Glow-in-the-Dark Rocks

Glow-in-the-Dark Rocks


Credit: Eden, Janine and Jim
Source: https://www.flickr.com/photos/edenpictures/6118545334/
License: CC BY-NC 3.0

If you walked around with an ultraviolet light, especially in parts of New Jersey, you might see a beautiful and eerie site. Glowing colored rocks!

Amazing But True!

  • Fluorescence is one of the unusual traits that help geologists to identify minerals.
  • These minerals fluoresce in ultraviolet (V) or black light.
  • There are 357 different types of fluorescent minerals in New Jersey; 24 of them are not found anywhere else.
  • Different minerals give off different colors.
  • Manganese (Mn) is present in willemite and calcite as an impurity. This impurity makes some of the rocks fluoresce.
  • Geologists think that these minerals may have come from underwater black smokers 1.3 billion years ago.
  • Credit: Parent G?ry. Edited by Robert Lopez.
    Source: http://commons.wikimedia.org/wiki/File:Chrysob%C3%A9ryl_var._alexandrite_(Madagascar)_.jpg; http://commons.wikimedia.org/wiki/File:Chrysob%C3%A9ryl_var._alexandrite_sous_UV_(Madagascar)_.jpg
    License: CC BY-NC 3.0

    Chrysoberyl crystal in natural light on the left, and under UV radiation on the right [Figure2]


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With the links below, learn more about fluorescent minerals. Then answer the following questions.

  1. What does UV light do to the electrons in these fluorescent minerals?
  2. What causes the electrons to give off light?
  3. Why does Mn cause a glow of different colors in different minerals?
  4. Not all fluorescent minerals glow because of Mn. What else may cause minerals to glow?
  5. What geological feature are the fluorescent minerals found with?

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