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Smithsonian National Museum of Natural History


Photograph of a rhomboidal carved moonstone (NMNH G4134) from the National Gem Collection with soft mirror
Photo by Chip Clark. Click to zoom.
Catalog Number NMNH G4134-00
Locality Sri Lanka
Weight 24.38 ct

From the exhibit

Look at these minerals from one direction, then another, to catch the play of light.

Labradorites, moonstones, and sunstones belong to the feldspar family, which makes up over half of the Earth’s crust. Occasionally, this common material forms crystals that shimmer like a rainbow on a soap bubble. This iridescence occurs when closely spaced layers in a crystal diffract light, separating it into its component colors.

Look for:

  • sunstones flashing golden orange (from flecks of goethite or copper).
  • a labradorite crystal with concentric bands of iridescent color.
  • moonstones, known for bluish-white iridescence.


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