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Where is Calcite with Pyrite found?

CaCO3 (Calcite) with FeS2 (Pyrite)

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Calcite 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 Calcite with Pyrite

Elmwood Mine, Carthage, Tennessee, USA

Known for world-class calcite crystals, often associated with sphalerite, fluorite, and sometimes pyrite.

Naica Mine, Chihuahua, Mexico

Famous for giant selenite crystals, but also produces calcite and pyrite in hydrothermal veins.

Various localities in Peru

Many Peruvian ore deposits yield excellent specimens of calcite and pyrite, often with other sulfides.

Dalnegorsk, Primorsky Krai, Russia

Produces large, well-formed calcite crystals, sometimes with associated pyrite.

Certain coal seams and shales worldwide

Pyrite concretions and crystals are common in anoxic sedimentary environments, often with calcite as a cementing agent or later infill.

Collecting tips

  1. Hydrothermal Veins. Look for these minerals in quartz or carbonate veins cutting through various rock types, especially in mining districts.
  2. Sedimentary Rocks. Examine shales, limestones, and coal deposits for concretions or disseminated crystals. Pyrite often forms in reducing conditions within these rocks.
  3. Acid Test for Calcite. Calcite will effervesce vigorously when a drop of dilute hydrochloric acid (HCl) is applied. Pyrite will not react.
  4. Hardness Test. Calcite (Mohs 3) can be scratched by a copper coin, while pyrite (Mohs 6-6.5) cannot and will scratch glass.
  5. Streak Test for Pyrite. Pyrite leaves a greenish-black to brownish-black streak on an unglazed porcelain plate, distinguishing it from gold (yellow streak).

Quick Check

Color:
Calcite: Variable, often white/colorless. Pyrite: Brassy yellow.
Luster:
Calcite: Vitreous. Pyrite: Metallic.
Streak:
Calcite: White. Pyrite: Greenish-black to brownish-black.

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