State by State


  • Specimen Number


  • Description

    Irregular boulder of complex rock that is likely a coarse igneous protolith with phenocrysts and pervasive hydrothermal alteration. Identified by staff from the State Geological Survey. Malachite stain on rim suggests bulk rock is metalliferous. It's possible the metal crystals were visible when the sample was collected, but have since oxidized.

  • Classification

    Complex. Hydrothermally altered protolith.  Ore. Silver.

  • Location & Occurrence

    Malachite and rust indicate likely ore from silver mines in southwestern state near Phillipsberg, confirming the Hartford Courant identification as "silver-bearing ore." The Connecticut Campus identified it as having come from Iowa.

  • Geologic Age

    Likely of Mesozoic age (synorogenic). Protolith and alteration have different ages.

  • Geoheritage

    Sample of Cordilleran ore illuminates the story of western mining.

  • Links

    Link to State Geological Map from USGS.  Link to Montana Bureau of Mines & Geology.

  • Other

    Mentioned as "silver-bearing ore" in Hartford Courant 1937, confirming informants speculation of location.


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Specimen stone for Montana.
Closeup of Montana Outline map of Montana Geo Map of Montana