Rockhounding in Fergus County, Montana

Sketch map

Woof’s favorite find

Spotted Horse Mine

We picked it because its USGS record mentions 4 gem or collectible minerals (Quartz, Gold, Fluorite, Silver) and 6 of our card minerals overall. No other named site here scores as high on both counts. USGS lists it as producer for Gold, Silver. Minerals mentioned: Quartz, Gold, Galena, Fluorite, Copper, Silver. Approx. location 47.176, -109.211. USGS record.

Ask first: a USGS record doesn’t mean you can visit. Find out who owns the land and get permission before collecting.

Field cards: what kind of sites?

Status terms come from USGS MRDS records.

Mineral cards

• Gold

  Mohs 2.5–3. Soft, heavy and bright yellow; it doesn’t tarnish. Mindat

  87 sites

• Silver

  Mohs 2.5–3. Native silver tarnishes black. Mindat

  68 sites

• Copper

  Mohs 2.5–3. Native copper is soft and turns green as it weathers. Mindat

  17 sites

• Fluorite

  Mohs 4. Cubes in purple, green or yellow; many glow under UV. Mindat

  11 sites

• Pyrite

  Mohs 6–6.5. Brassy “fool’s gold,” often cubic. Mindat

  6 sites

• Galena

  Mohs 2.5–2.75. Heavy, silvery lead ore that breaks into cubes. Mindat

  4 sites

• Magnetite

  Mohs 5.5–6.5. Black and strongly magnetic. Mindat

  2 sites

• Quartz

  Mohs 7. Six-sided points; smoky quartz is NH’s state gem. Mindat

  1 site

Counts are sites whose USGS record mentions the mineral or commodity. Hardness from Mindat.

How we built this page: we counted named sites in the USGS Mineral Resources Data System (MRDS) for this area, left out sand, gravel, crushed stone, clay pits and unnamed sites, grouped them by Census county, and linked every site to its USGS record. We did not visit these sites, and MRDS does not tell you who owns the land or whether collecting is allowed.

Source: USGS Mineral Resources Data System (MRDS). USGS ceased systematic updates to MRDS around 2011, so status and details may be out of date. Each site links to its USGS record.

Updated October 2026