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Where is Crushed aggregate with pyrite found?

Mixed rock fragments with Pyrite (FeS2)

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Crushed aggregate with pyrite 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 Crushed aggregate with pyrite

Quarries and Mines

Any quarry or mine extracting rock for aggregate production that happens to contain pyrite-bearing strata. This is a global issue, with occurrences reported in North America (e.g., Canada, USA), Europe (e.g., Ireland, UK, Scandinavia), and Australia.

Construction Sites

Areas where pyritic aggregate has been used in concrete, road base, or fill. Deterioration due to pyrite oxidation can manifest as cracking, swelling, and staining.

Collecting tips

  1. Visual Inspection. Look for brassy yellow, metallic specks or crystals within the crushed rock fragments. These can range from microscopic to several millimeters in size.
  2. Acid Test (Caution Advised). While not definitive for pyrite, applying a drop of dilute hydrochloric acid (HCl) to the aggregate can help identify carbonate rocks (which will effervesce). Pyrite itself does not react with dilute HCl, but its presence in carbonate aggregate can be problematic. This test should be done with appropriate safety precautions.
  3. Geological Context. Understand the geology of the aggregate source. If the source rock is known to contain pyrite (e.g., black shales, certain limestones, or rocks from mineralized areas), the aggregate is likely to contain it.

Quick Check

Color:
Brassy yellow (for pyrite), variable for host rock
Luster:
Metallic (for pyrite), variable for host rock
Streak:
Greenish-black to brownish-black (for pyrite)

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