Delaware is okay state for rockhounding. Delaware occasionally is referred to as "The Diamond State" because Thomas Jefferson once referred to it as a jewel due to its geographic location. There are, however, no diamonds there. Delaware does have a variety of fossils and some petrified wood. In addition, the state has some interesting mica specimens.
State Rocks, Gemstones, Minerals, Fossils, & Dinosaurs
Rockhounding Tip: Knowing state rocks, gemstones, minerals, fossils, and dinosaurs often can be very useful information for rockhounders. Ordinarily, states with significant mineral deposits, valuable gemstones, fossils, or unusual or significant rock occurrences will designate an official state mineral, rock/stone, gemstone, fossil, or dinosaur to promote interest in the state’s natural resources, history, tourism, etc. Accordingly, such state symbols often are a valuable clue as to potential worthwhile rockhounding opportunities.
Mineral: Sillimanite (1977)
Delaware designated sillimanite as its official state mineral in 1975. Sillimanite is aluminum silicate that occurs in high temperature, aluminum-rich metamorphic rocks. Sillimanite is a polymorph with kyanite and andalusite. It may take the form of clear or gray-white glassy crystals or form fibrous masses with a silky luster. In Delaware, sillimanite is widespread throughout the schists of the Delaware Piedmont and occurs as large masses and stream-rounded boulders at the Brandywine Springs State Park. Sillimanite has no industrial value and is not mined as an ore or raw material. The mineral is named is in honor of Benjamin Silliman, a professor of Chemistry and Natural History at Yale University from 1802 - 1853.
State Fossil: Belemnite (1996)
Delaware designated belemnite as its official state fossil in 1996. The belemnite was, in essence, a squid with a conical shell. It is an extinct member of the phylum Mollusca, which includes clams, snails, squids and octopuses. Belemnite fossils can be found in dredging piles from the creation of the Chesapeake and Delaware Canal.
State-specific rockhounding books (including the books listed here as well as other books), regional rockhounding site guides, and other helpful rockhounding resources are identified - by category - in the Books & Gear section of Gator Girl Rocks with a link to the Gator Girl Rocks Amazon Store where you may easily browse selected resources and securely place an order. Your order will benefit Charity Rocks!
Good information on cretaceous fossils found in Delaware. The DGS also has special publications pertaining to Delaware rocks, minerals, and fossils.
Website for the Delaware Mineralogical Society. This rockhounding club has a very useful website.
- John Means, Roadside Geology of Maryland, Delaware, and Washington DC (2010).
- James Martin Monaco & Jeannette Hathway Monaco, Fee Mining & Mineral Adventures in the Eastern U.S. (2d ed. 2010).
- Kathy J. Rygle & Stephen F. Pedersen, Northeast Treasure Hunter's Gem & Mineral Guide (4th ed. 2008).
Museums of Interest to Rockhounders
Delaware Mineralogical Museum
University of Delaware – Newark, Delaware
The Mineralogical Museum in Penny Hall originated with the gift of the Irenée du Pont, Sr. collection in 1964. A significant part of this collection was purchased in 1919 by Mr. du Pont from George Kunz, Vice-President of Tiffany & Co, and had been on display in the Tiffany showroom in New York City.
Delaware Museum Of
The Delaware Museum of Natural History’s Dinosaur Gallery showcases the only dinosaurs on permanent display in the state. The towering dinosaur skeletons, Tuojiangosaurus and Yangchuanosaurus, represent Asian relatives of the familiar North American dinosaurs, Stegosaurus and Allosaurus. A Parasaurolophus head and Archaeopteryx are also on display. The Dinosaur Gallery includes the Science in Action Lab, where volunteers prepare real paleontology specimens for study and answer visitor questions.
Iron Hill Museum
Delaware Academy of Science – Newark, Delaware
The museum houses part of the du Pont Rock and Mineral collection, which displays rocks and minerals from around Delaware and around the world. In addition, the museum’s exhibits include iron mining, petrified wood, fossils, and fluorescent minerals.
Places to Visit - Interesting Sites To See
Brandywine Blue Granite
Brandywine Creek State Park – North of Wilmington, Delaware
Wilmington blue rock (Brandywine Blue Gneiss of the Wilmington Complex) is visible in the park. Naturally, the rocks will appear dark gray or black, but, when quarried and fresh cuts are exposed, the rocks have a bright blue color. Garnets occur in the blue gneiss.
This site is where the initial Swedish landing took place and where the New Sweden colony began. In 1638 two ships (the Kalmar Nyckel and the Fogel Grip) sailed up the Christina River past the entrance to the Brandywine to "The Rocks" where a large flat slab of blue rock protrudes into the main channel of the river. The large flat slab of rock on which the early settlers landed, although reduced to make room for river travel on the Christina, is still a present in Swedes Landing Park. "The Rock" is a slab of Wilmington Complex gneiss or blue rock, and marks the eastern edge of exposure of the Appalachian mountain system where the hard rocks of the Piedmont Province plunge beneath the soft sediments of the Coastal Plain. The boundary between the Piedmont and the Coastal Plain is defined in most places by a well-marked change in topography, usually an abrupt transition from rolling hills to a flat smooth lowland.
Rockhounding Sites for Children & Families
Chesapeake and Delaware Canal
Belemnite fossils can be found in the exposures of the Mount Laurel Formation along the banks of the Chesapeake and Delaware Canal in Delaware, east of St. Georges. The fine-grained sands and silts of the Mount Laurel were deposited in a shallow sea during the Late Cretaceous time around 70 million years ago.
Northern Delaware has sites with muscovite mica that can form ‘mica books.’ The Woodlawn Quarry is a well-known site.