Where is Tourmaline Granite found?
Granite (igneous rock) with Schorl (black tourmaline)
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Open the appTourmaline Granite 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 Tourmaline Granite
Cornwall, England
Famous for its tourmaline-rich granites and associated tin-tungsten mineralization, particularly the Carnmenellis and Bodmin Moor granites.
Brazil
Various states, including Minas Gerais, are renowned for pegmatites and granites containing abundant tourmaline, often of gem quality, but also schorl.
United States
Localities in Maine (e.g., Mount Mica), California (e.g., Pala District), and Colorado are known for tourmaline-bearing granites and pegmatites.
Africa
Countries like Namibia and Madagascar have significant occurrences of tourmaline-bearing granites and pegmatites.
Australia
Western Australia and other regions host granitic intrusions with tourmaline, often associated with mineral deposits.
Collecting tips
- Look for Plutonic Environments. Focus on areas known for large intrusive igneous bodies, such as batholiths or stocks, especially in ancient mountain belts or continental shields.
- Identify Boron-Rich Zones. Tourmaline is a boron-silicate. Look for granites associated with pegmatites, aplites, or areas showing signs of hydrothermal alteration, as these environments are often enriched in boron.
- Recognize Schorl's Characteristics. Schorl (black tourmaline) is easily identifiable by its black color, prismatic habit, often with vertical striations, and triangular cross-section. It stands out against the lighter-colored granite matrix.
- Examine Outcrops and Road Cuts. Freshly exposed rock surfaces in quarries, road cuts, and stream beds often provide the best views of mineral textures and compositions.
- Use a Hand Lens. A hand lens (10x magnification) will help in identifying the individual mineral grains, their crystal forms, and the characteristic striations on tourmaline.
Quick Check
- Color:
- Light-colored matrix (white, gray, pink) with distinct black, prismatic crystals.
- Luster:
- Vitreous to resinous for tourmaline; vitreous for quartz; pearly to vitreous for feldspar.
- Streak:
- White (for quartz and feldspar); colorless (for tourmaline, though it's too hard to streak easily).
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