Union County: Agate & Apophyllite Rockhounding in Somerset County, New Jersey

Updated June 2026

Union County is a mapped rockhounding spot in Somerset County, New Jersey. Reported finds include agate, apophyllite, albite, bornite, chalcedony, and more. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Somerset County
State: New Jersey
Nearest road: Valley Road
Postcode: 07069
Coordinates: 40.66022, -74.40913

Geology at Union County

This spot sits on Orange Mountain Basalt, mapped as basalt that formed roughly 200 to 175 million years ago. Volcanic ground like this is where agate, jasper, and other chalcedony typically form, filling old gas pockets and fracture seams in the flow rock.

Mapped unit: Orange Mountain Basalt
Age: 200–175 Ma (Early Jurassic)
Rock types: basalt
Elevation: 220 ft

Geologic mapping via Macrostrat and the underlying state geological survey maps (CC BY 4.0). Bedrock at the surface can vary within a mapped unit.

Best time to visit Union County

Best months: March to December. Typical highs run 88°F in midsummer and 40°F in midwinter, with winter lows near 23°F.

Climate normals: NOAA 1991-2020 monthlies, PLAINFIELD station (4 mi away).

Land & collecting status

Generally open to casual rockhounding

Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig.

Public-land rules vary by agency, season, and field office. The RockHoundR app pulls live BLM, USFS, NPS, and tribal overlays so you can see exactly which agency manages the ground at this spot.

Sources & verification

Spot details combine the public RockHoundR location dataset, normalized mineral labels, agency land-status checks in the app, and community submissions. Coordinates are approximate until verified in the field.

Sources: RockHoundR public spot dataset, app land overlays, and local agency review before each trip.

Found at Union County

Each chip opens all spots that produce that material; the encyclopedia link opens the full ID and field guide.

Nearby rockhounding spots

Other rockhounding spots within driving distance of Union County.

Across the state line from Union County

Union County is close enough to the New Jersey border that the next-closest rockhounding spots are in a neighboring state. Worth knowing if you are already on the road.

Union County FAQ

Where is Union County?+

Union County is in Somerset County, New Jersey, at 40.66022, -74.40913. Nearest road: Valley Road.

What rocks and minerals can you find at Union County?+

Union County is reported to produce Agate, Apophyllite, Albite, Bornite, Chalcedony, Datolite, Galena, Hematite, Opal.

Is collecting allowed at Union County?+

Generally open to casual rockhounding. Most public-tagged spots sit on BLM, U.S. Forest Service, or other federal land where reasonable hand collecting of common rocks and minerals is allowed. Confirm posted rules and active mining claims before you dig. Always confirm current rules with the managing agency before a trip.

What tools should I bring to Union County?+

Most agate and jasper is surface float: bring a spray bottle, a pick or small shovel, and a sturdy bag. Wet stones show their banding and translucence.

When is the best time to visit Union County?+

The most comfortable months at Union County are March to December.

How do I get to Union County?+

Open the directions link to navigate to 40.66022, -74.40913 in Google Maps. The nearest road is Valley Road.

More rockhounding in New Jersey

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Open Union County on the map

Use the RockHoundR app for live land overlays, weather, geology, directions, and saved finds.