Rockhounding in Baltimore County, Maryland

Sketch map

Woof’s favorite find

Choate Mine

We picked it because its USGS record mentions 1 gem or collectible mineral (Agate) and 1 of our card minerals overall. That ties with 1 other site(s), so we broke the tie by mine status (past producers first), then USGS record quality, then name. USGS lists it as past producer. Minerals mentioned: Agate. Approx. location 39.412, -76.834. 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

• Feldspar

  Mohs 6–6.5. Blocky crystals with flat cleavage faces. Mindat

  32 sites

• Magnetite

  Mohs 5.5–6.5. Black and strongly magnetic. Mindat

  4 sites

• Copper

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

  3 sites

• Quartz

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

  1 site

• Agate

  Mohs 6.5–7. Banded, translucent chalcedony. Mindat

  1 site

• Pyrite

  Mohs 6–6.5. Brassy “fool’s gold,” often cubic. 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 USGS ceased systematic updates to MRDS around 2011, so status and details may be out of date.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