Delaware mineralogical society

A Delaware 501(c)(3) non-profit earth-science educational organization


Brandywine Springs County Park, Wilmington, DE


Delaware Mineralogical Society
Field Trip
May 7, 2016
Brandywine Springs County Park

The Delaware Mineralogical Society (DMS) will host a field collecting trip to BRANDYWINE SPRINGS PARK on May 7, 2016. This trip is for DMS members only and members of invited clubs. This site is principally known for rather large specimens of the metamorphic mineral sillimanite, the Delaware State mineral. Also found at this site is smoky quartz associated with sillimanite, garnets may be panned from the Red Clay Creek, and ringing quartzite.

Here’s a report of a previous trip.

We started the day at Brandywine Springs Park. Brandywine Springs Park is famous for both having the only natural cave in Delaware and large specimens of the state mineral sillimanite. We met in the parking lot, walked across the baseball fields and into the woods to the large sillimanite boulder that’s slated to be moved to the Delaware Museum of Natural History(since moved).

Though significantly weathered and moss and lichen covered on its exposed surface, it gave everyone a good idea of what the mineral looks like ‘in the wild’. It’s not as easy to identify and find sillimanite as one might imagine.

We then hiked down to the cave. The cave is at the boundary of the Wilmington Complex and the Wissahickon Formation and 3 rock types meet here; quartzite, amphibolites and a soft schist. The schist has eroded to make the cave which is about 5’ wide and 5’deep. The quartzite is particularly dense and produces a nice ‘ring’ when thumped with a hammer.

We then hiked to Hyde Run creek to search for sillimanite. Ken found the first specimen in route to the cave, and more were found by Jose, John, Mary Ann and Tom in the creek. Jose also captured a bull frog…amphibolite and amphibian kinda sound alike? Several more specimens were found on the hillside above the creek so everyone got one for their collection (Note: permission must be obtained to collect in the park).

And now some more information:

1. This trip is mostly looking closely and picking up rocks. Bring no tools other then perhaps a hoe like scraper. There is no digging at this site. If you create a hole by dislodging a specimen, refill the hole. Don’t bring a hammer as there’s no breaking of rocks either. This is a ‘leave no trace’ trip.

2. Bring water boots; sillimanite is most frequently found in Hyde Run (a few feet wide, inches deep) and on the gravel bars in adjacent Red Clay Creek (wider and deeper).

3. Bring a pan: there’s lots of garnet sand along Red Clay Creek. This garnet can also be collected with a strong rare earth magnet held inside a plastic bag. You’ll also get a lot of iron oxide which can be removed later by tumbling (garnet >> harder than iron oxide).

4. Meeting time and location will be sent at a later date to registered participants.

5. Do not collect at this site on your own. It is a New Castle County Park and collecting without permission is forbidden.

6. The site is shady and there are few mosquitoes (I’ve never seen one, but no doubt writing this will bring out legions). The walk from parking to collecting is about 100 yds across a grass field then down a ravine on well-hiked paths. On the way you’ll see some of the biggest tulip poplars I’ve ever seen.

7. Participants will be asked to sign a Liability Waiver.

8. Only 1 specimen is allowed per participant. If you find 2, either gift one to somebody less fortunate or return it to the wild. Please keep just 1 specimen…thank you. (for example, since already have 1 I will keep none, but I might share a few).

9. If you find one, show you buddies. You’d be surprised how hard it is to ‘see’ sillimanite covered in mud. I will bring a specimen to help ‘train’ your eyes. Not all sillimanite looks like fibrolite; some is surprisingly ‘feldspar-looking’.

10. If you wish to participate, contact Tom Pankratz by email ( I’ll send you a confirming email. If I don’t, recontact me.

11. And contact me if you’ve a question.

--Tom Pankratz