Near Brandywine Springs State Park: Sillimanite Rockhounding in New Castle County, Delaware

Plan your visit

Permission required before collecting

County

New Castle County

State

Delaware

Nearest road

Thompsons Bridge Road

Postcode

19803

Coordinates

39.80872, -75.57681

Coordinates are approximate. Confirm the exact ground in the RockHoundR app, where land overlays show which agency manages the area.

Land & collecting status

Permission required before collecting

Requires landowner or agency permission before any collecting. Do not enter without explicit authorization.

Access note: This is the hardest of Delaware's identity spots to collect legally: the historic sillimanite ground lies on state-park land (Brandywine Springs and Brandywine Creek State Parks, no collecting) and private property, and the nearby Hoopes Reservoir is a fenced public water supply with access limited by law. The Delaware Geological Survey itself points collectors to the Delaware Mineralogical Society for specimens rather than to an open site. Enjoy it as a look-and-learn locality, do not trespass on reservoir or private land, and seek permission for any private outcrops.

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.

Best time to visit Near Brandywine Springs State Park

Comfortable months (45 to 90°F highs)

Best months: March to November. Typical highs run 84°F in midsummer and 37°F in midwinter, with winter lows near 23°F.

Climate normals: NOAA 1991-2020 monthlies, WILMINGTON PORTER RSCH station (3 mi away).

Geology at Near Brandywine Springs State Park

This spot sits on Wissahickon Schist, mapped as schist and gneiss that formed roughly 540 to 250 million years ago. Metamorphic rock like this is where garnet, staurolite, and kyanite typically grow as the rock recrystallizes under heat and pressure.

Mapped unit

Wissahickon Schist

Age

540–250 Ma (Paleozoic)

Rock types

schist and gneiss

Elevation

390 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.

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.

• Delaware Geological Survey
• Delaware State Parks rules
• Community submissions reviewed against published agency rules