Houdaille Quarry: Agate & Prehnite Rockhounding in Union County, New Jersey

Updated June 2026

Houdaille Quarry is a mapped rockhounding spot in Union County, New Jersey. Reported finds include agate, prehnite, amethyst. Below: coordinates, access notes, nearby spots, and trip-planning links.

Quick details

Access: Public area
County: Union County
State: New Jersey
Nearest road: Phillipsburg-Newark Expressway
Postcode: 07081
Coordinates: 40.71001, -74.33479

Geology at Houdaille Quarry

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: 270 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 Houdaille Quarry

Best months: March to November. Typical highs run 86°F in midsummer and 39°F in midwinter, with winter lows near 22°F.

Climate normals: NOAA 1991-2020 monthlies, CANOE BROOK station (3 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 Houdaille Quarry

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 Houdaille Quarry.

Across the state line from Houdaille Quarry

Houdaille Quarry 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.

Houdaille Quarry FAQ

Where is Houdaille Quarry?+

Houdaille Quarry is in Union County, New Jersey, at 40.71001, -74.33479. Nearest road: Phillipsburg-Newark Expressway.

What rocks and minerals can you find at Houdaille Quarry?+

Houdaille Quarry is reported to produce Agate, Prehnite, Amethyst.

Is collecting allowed at Houdaille Quarry?+

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 Houdaille Quarry?+

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 Houdaille Quarry?+

The most comfortable months at Houdaille Quarry are March to November.

How do I get to Houdaille Quarry?+

Open the directions link to navigate to 40.71001, -74.33479 in Google Maps. The nearest road is Phillipsburg-Newark Expressway.

More rockhounding in New Jersey

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Open Houdaille Quarry on the map

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