Where is Moonstone found?
Orthoclase feldspar (variety adularia)
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Open the appMoonstone occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Moonstone
Sri Lanka
Historically a primary source of high-quality blue moonstone, particularly from the Meetiyagoda mines.
India
Produces significant quantities of moonstone, often with a peach or rainbow adularescence.
Myanmar (Burma)
Known for producing fine moonstone.
Madagascar
A source of various feldspar varieties, including moonstone.
Tanzania
Produces moonstone, sometimes with a cat's eye effect.
Brazil
Some occurrences of moonstone have been reported.
United States (e.g., New Mexico, Virginia, Pennsylvania)
Localities where orthoclase and adularia have been found, some exhibiting adularescence, though not always gem quality.
Switzerland (Adula Alps)
The type locality for adularia, where it was first described.
Collecting tips
- Look for Hydrothermal Veins. Moonstone (adularia) often forms in low-temperature hydrothermal veins. Search for areas with quartz veins or fissures in igneous or metamorphic rocks.
- Examine Pegmatites. While less common for adularia, some moonstone can be found in pegmatite dikes, which are coarse-grained igneous rocks. Look for large feldspar crystals.
- Check for Associated Minerals. Moonstone is often found with other minerals like quartz, albite, and other feldspars. Identifying these associated minerals can indicate a favorable environment.
- Observe Optical Effects. The most distinctive feature is adularescence. Rotate potential specimens under a light source to look for the characteristic bluish-white sheen that glides across the surface. This is best observed on smooth, fractured, or polished surfaces.
- Consider Hardness. With a Mohs hardness of 6-6.5, moonstone can be scratched by harder minerals like quartz. This can help differentiate it from harder look-alikes.
Quick Check
- Color:
- Colorless to white, gray, peach, yellow, blue, with adularescence.
- Luster:
- Vitreous to pearly.
- Streak:
- White.
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