Where is Moonstone found?
Adularia (Potassium Feldspar)
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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 (Ceylon)
Historically the most important source, producing fine blue moonstone. Found in pegmatites and alluvial deposits.
India
Known for producing 'rainbow moonstone' (which is actually labradorite) and peach/gray moonstone. Found in pegmatites and metamorphic rocks.
Myanmar (Burma)
Produces high-quality moonstone, often with a strong blue sheen.
Madagascar
A source of various colors of moonstone, including white, gray, and peach.
Tanzania
Known for producing moonstone with good adularescence.
United States (e.g., New Mexico, Virginia, Pennsylvania)
Localities where adularia and other feldspars exhibiting adularescence can be found, often in pegmatites or hydrothermal veins.
Brazil
Produces some moonstone, often in pegmatitic environments.
Switzerland (Adula Alps)
The type locality for Adularia, where it was first described. Found in alpine-type fissures.
Collecting tips
- Look for Feldspar Environments. Search in areas known for pegmatites, hydrothermal veins, and alpine-type fissures, as these are common environments for feldspar formation, including moonstone.
- Examine for Adularescence. The key identifying feature is the adularescence. Rotate potential specimens under a light source to observe the characteristic floating blue or white sheen. This is best seen on smooth, rounded surfaces.
- Check for Cleavage. Feldspars exhibit perfect cleavage in two directions at nearly 90 degrees. Look for these flat, reflective surfaces on broken specimens.
- Consider Hardness. Moonstone has a Mohs hardness of 6-6.5, meaning it can be scratched by quartz (7) but will scratch glass (5.5). This can help differentiate it from softer minerals.
- Distinguish from Similar Minerals. Be careful not to confuse it with opal (which has play-of-color, not adularescence, and is softer) or labradorite (which exhibits labradorescence, a broader spectrum of iridescent colors, and is a plagioclase feldspar).
Quick Check
- Color:
- Colorless to white, gray, peach, with a characteristic bluish-white sheen (adularescence).
- Luster:
- Vitreous to pearly.
- Streak:
- White.
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