Where is Shale with Calcite and Marcasite found?

Shale with Calcite and Marcasite 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 Shale with Calcite and Marcasite

Collecting tips

1. Look for Dark, Fissile Rocks. Shales are typically dark and split easily into thin layers. The presence of lighter calcite or metallic marcasite will be visible within this matrix.
2. Check for Metallic Luster. Marcasite's brassy to silvery metallic luster is a key indicator. It often forms distinctive radiating or nodular shapes.
3. Acid Test for Calcite. A drop of dilute hydrochloric acid (HCl) will effervesce on calcite, indicating its presence. Be cautious with acid and wear appropriate safety gear.
4. Examine Associated Strata. These shales are often found in association with coal seams, organic-rich layers, or marine fossiliferous beds, indicating the anoxic and carbonate-rich conditions of their formation.
5. Beware of Weathering. Marcasite is unstable in oxygenated, moist environments and will weather to iron oxides and sulfuric acid. Fresh samples are best found in unweathered outcrops or excavations.

Quick Check

Color:

Dark gray to black shale matrix; brassy yellow to silvery-white marcasite; white to gray calcite.

Luster:

Dull to earthy for shale; metallic for marcasite; vitreous to dull for calcite.

Streak:

Shale: white, gray, or black (depending on composition). Marcasite: greenish-black to brownish-black. Calcite: white.

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