By Trista L. Pollard /
1In Mineral Detectives, Part I, we discussed the physical properties of minerals and how mineralogists use these properties to identify unknown minerals. In this article we will explore a few special properties of minerals that are used by scientists as they solve the "mineral mystery." These special properties are fluorescence, phosphorescence, chatoyancy, asterism, double refraction, magnetism, and radioactivity.
2Some minerals appear a certain way in ordinary light. However, when they are placed under ultraviolet light, their color changes, and they appear to glow. This quality is called fluorescence. When minerals have the quality of fluorescence, they produce light that has different colors under ultraviolet light. If you were to hold the mineral calcite in ordinary light, you would notice that it appears white. However, place that same mineral under ultraviolet light, and it will appear red. A few minerals on Earth not only glow under ultraviolet light, but they continue to glow for a period of time after they are removed from ultraviolet light. This property is called phosphorescence. The mineral eucryptite, an ore of lithium, is phosphorescent.
3Minerals that have the property of chatoyancy appear to have a silky appearance when light is reflected off the mineral. Scientists refer to this as the cat's-eye effect. This effect occurs because the mineral has fibers that are parallel and closely packed together. If a mineral has a six-sided star shape as it reflects light, this is called an asterism. Transparent minerals display another type of physical property called refraction. When the light passes through a transparent mineral, the light rays bend or refract. Some minerals like calcite display double refraction as the light passes through. Double refraction occurs when the bending or refracting of the light causes any object viewed through the mineral to appear as a double image. As the light rays pass through the crystal mineral, the rays are split. This causes the double image to appear.
4Magnetism and radioactivity are properties scientists may look for as they try to identify minerals. Some minerals have traces of iron mixed in with other elements. These minerals may be magnetic like the nonsilicate mineral magnetite. In fact, you have probably heard of lodestones, which are magnetic and a form of magnetite. This is when using a magnet would come in handy for identifying these types of minerals. Other minerals have the property of radioactivity. An atom's arrangement of protons and neutrons may cause its nucleus to be unstable. That atom becomes radioactive when the unstable nuclei decay into stable nuclei over time. As the decay occurs, particles and energy are released. Scientists can use Geiger counters to identify and detect minerals that release radioactive particles. This means that the minerals contain elements like uranium (U) and radium (Ra), which are radioactive. The mineral carnotite, which contains uranium, is radioactive. As you have learned there are many methods and clues that mineralogists can use to identify minerals. So the next time you think your rock is a mineral, try using some of these properties to solve your "mineral mystery."
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Mineral Detectives, Part II1. / Phosphorescent minerals ______.
Have a six-sided star shape in reflected light
Glow under ultraviolet light and reflect light of different colors
Continue to glow after they are removed from ultraviolet light
None of the above
/ 2. / Compare refraction and double refraction.
3. / Explain how knowing the property of fluorescence and phosphorescence would help miners when they are mining for ore.
/ 4. / Radioactive minerals contain traces of radium and/or ______.
5. / What is chatoyancy? How is chatoyancy different from asterism?
/ 6. / Complete the sentence: Another name for asterism is ______.
Minerals that absorb ultraviolet light and glow in light of various colors have the property of _____.