Where is Corundum found?
Al₂O₃
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Open the appCorundum 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 Corundum
Myanmar (Burma)
Famous for high-quality rubies (Mogok Valley) and sapphires.
Sri Lanka
Known for a wide variety of sapphires (blue, pink, yellow, padparadscha) and rubies, often found in alluvial deposits.
Thailand
Historically significant for rubies and blue sapphires, particularly from Chanthaburi and Trat provinces.
Cambodia
Produces rubies and sapphires, often associated with basaltic rocks.
Madagascar
A major source of sapphires (blue, pink, yellow, green) and rubies, found in various geological settings.
Australia
Significant producer of blue and yellow sapphires, especially from Queensland and New South Wales.
United States
Localities in Montana (Yogo Gulch for blue sapphires, Rock Creek for various colors) and North Carolina (rubies and sapphires in metamorphic rocks).
India
Historical source of rubies and sapphires, particularly from Kashmir (famous for 'cornflower blue' sapphires).
Tanzania
Produces rubies (e.g., Winza, Longido) and sapphires (e.g., Tunduru, Umba Valley).
Kenya
Known for rubies and sapphires.
Collecting tips
- Look in Placer Deposits. Due to its high specific gravity and hardness, corundum often concentrates in alluvial (placer) deposits. Look for gravels in stream beds, ancient river terraces, and weathered eluvial deposits derived from primary sources.
- Identify Associated Minerals. In primary metamorphic settings, corundum can be found with minerals like kyanite, sillimanite, andalusite, garnet, spinel, mica, and feldspar. In igneous settings, it may be associated with nepheline, feldspathoids, and amphiboles.
- Check for Hexagonal Crystal Forms. Corundum often forms distinctive hexagonal prismatic or barrel-shaped crystals. Look for these characteristic shapes, even in weathered or broken fragments.
- Test Hardness. Corundum is extremely hard (9 on Mohs scale). It will scratch almost all other common minerals, including quartz. This is a key diagnostic property, but be cautious not to damage valuable specimens.
- Examine for Parting. While not true cleavage, corundum often exhibits parting. Look for flat, parallel planes of weakness within the crystal, which can sometimes be mistaken for cleavage.
- Consider Geological Context. Focus your search in regions known for silica-deficient igneous rocks or high-grade metamorphic terrains, especially those with aluminum-rich protoliths.
Quick Check
- Color:
- Highly variable (red, blue, yellow, green, colorless, etc.)
- Luster:
- Vitreous to adamantine
- Streak:
- White
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