Where is Granite with Iron Staining found?
Granite (felsic intrusive igneous rock) with iron oxide staining
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Open the appGranite with Iron Staining 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 Granite with Iron Staining
Sierra Nevada Batholith, USA
Extensive granite exposures, where weathering processes can lead to significant iron staining, particularly in areas with abundant biotite or other iron-rich accessory minerals.
Appalachian Mountains, USA
Numerous granite plutons and batholiths, often exposed to prolonged weathering, resulting in widespread iron staining.
Cornwall, UK
Granite intrusions, particularly those associated with mineralization (e.g., tin, copper), can exhibit pronounced iron staining due to the oxidation of sulfide minerals like pyrite.
Brazilian Shield, Brazil
Ancient granite terrains where deep weathering profiles often show intense iron staining.
Collecting tips
- Look for Exposed Outcrops. Granite with iron staining is most commonly found in exposed bedrock outcrops, road cuts, quarries, and riverbeds where weathering has had an opportunity to act on the rock.
- Identify Primary Granite Features. First, confirm the rock is granite by identifying its characteristic coarse-grained texture and the presence of quartz, feldspar, and mica. Then, look for the secondary coloration.
- Observe Color Variation. Note the reddish, orange, or brownish hues that are distinct from the typical white, gray, or pink of unstained granite. The staining might be more intense along fractures or in areas where iron-rich minerals are concentrated.
- Consider the Environment. Iron staining is a weathering product, so it's more prevalent in areas that have been exposed to the elements for extended periods, especially in humid or temperate climates.
Quick Check
- Color:
- Light-colored granite (white, gray, pink) with secondary reddish, orange, or brown staining.
- Luster:
- Vitreous to dull for primary minerals, often earthy or dull in stained areas.
- Streak:
- White for quartz and feldspar, but the iron oxide staining itself will produce a reddish-brown to yellowish-brown streak if scraped on an unglazed porcelain plate.
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