Where is Weathered Granite found?
Granite (weathered)
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Open the appWeathered 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 Weathered Granite
Appalachian Mountains, USA
Extensive granite intrusions throughout the Appalachian chain exhibit significant weathering, particularly in the Piedmont region, forming deep saprolite profiles.
Sierra Nevada, California, USA
Granitic batholiths show varying degrees of weathering, with grus (decomposed granite) being a common surficial material, especially in areas of exfoliation and chemical alteration.
Brazilian Shield
Tropical and subtropical climates have led to very deep and intense weathering of granitic rocks, forming thick saprolite layers.
Western Australia
Ancient granitic terrains often display deep weathering profiles, sometimes associated with lateritic development.
Collecting tips
- Look for outcrops of granite. Weathered granite will always be found in association with fresh granite bedrock. Look for areas where granite is known to occur.
- Observe changes in rock integrity. Test the rock's hardness and coherence. If it crumbles easily, feels soft, or individual grains can be scraped off with a fingernail (for feldspars), it's likely weathered.
- Note color variations and staining. Dull colors, reddish-brown or yellowish staining, and a general lack of the vibrant colors seen in fresh granite are indicators of weathering.
- Examine individual mineral grains. Look for dull, opaque, or chalky feldspars, and altered mafic minerals. Quartz will typically retain its glassy luster but may be dislodged easily.
- Check for saprolite or grus. In deeply weathered areas, the granite may be completely disaggregated into a sandy, clay-rich soil-like material (grus or saprolite) that still retains the relict texture of the original granite.
Quick Check
- Color:
- Dull, often stained (brown, yellow, red), less vibrant than fresh granite.
- Luster:
- Dull to earthy for altered minerals, vitreous for quartz.
- Streak:
- White to light grey (for quartz and feldspar), reddish-brown for iron oxides.
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