Radiation Detector

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Radiation Detector - smoky quartz

Some minerals change colour when exposed to radiation
So some coloured minerals are, in effect, "radiation detectors" - they tell us they were once exposed to radiation.
The coloured irradiated minerals are generally not radioactive themselves.
However be cautious - the rocks that contain the minerals may be radioactive.
Elements are made up of protons, neutrons and electrons. Put very simply - radioactive elements contain too many bits inside to remain stable so from time to time they get rid of bits - this is called radiation.

The colour of smoky quartz is caused by irradiation and traces of aluminum built into its crystal lattice.
In normal geological environments this process can only take place at temperatures below 50°C
True smoky quartz will loose its colour when heated to about 200°C, and the colour will occur again when the crystal is irradiated with x- or gamma-rays. Some (but reportedly not all) smoky quartz is sensitive to ultraviolet light and will pale when exposed to sunlight for a long time
It's still common practice to artificially irradiate colourless quartz and sell it as smoky quartz.
There is no radiation hazard associated with irradiated smoky quartz. Irradiating a crystal will cause some energy to be stored in the crystal structure, which can change the optical properties, typically observed as a change in colour.

Using radiation to change the colour of gemstones has been studied almost as long as radioactivity has been known. An early study, published within 10 years of the discovery of radioactivity, placed diamonds in radium powder to give a green colour. As the use of radiation has become more sophisticated, the ability to treat gemstones with radiation in order to create colour changes has become more common.

Some minerals that are "radiation dectectors include...
  • Fluorite is irradiated to intensify its colour or induce colour (notably blue), usually by gamma rays from Cobalt-60 source.

  • Beryl - beryl is heated to remove the golden to green shades that result from radiation in oder to turn the crystal into blue aquamarine

  • Calcite - Radiation is associated with blue and amber colours of calcite

  • Diamond - Naturally occurring green diamonds are coloured by natural radiation, yellow diamond, 47K; A technological product of irradiation and heating. orange diamond, 53K; A technological product of irradiation and heating. blue diamond, 29K; A technological product of irradiation. Although they look similar to natural blue diamonds, the colour is from an entirely different origin. green diamond, 68K; A technological product of irradiation.

  • Halite (salt) - blue halite from Germany is the result of exposure to natural radiation

  • Quartz - will also turn purple and is known as amethyst is the result of natural irradiation of Fe3+ in the quartz to Fe4+. The purple amethst colour will fade in time when exposed to sunlight

  • Topaz - turns a brown colour but this colour is unstable and fades in light in a matter of hours to days Halite (salt) turns blue Calcite turns honey brown

  • Learn more about IGNEOUS ROCKS and MINERALS