Official State Fossil of Delaware
Belemnite is the official state fossil of Delaware. Belemnite fossils can be found easily along the shores of the Chesapeake and Delaware Canal. The canal is periodically dredged for navigation and the fossils can be found in the dredged material laid on the banks. This site was a favorite of my in-laws. It is fairly easy pickings but if it has been rainy wear boots.
The Delaware Geological Survey has information and maps to accessible digging sites here: Delaware Fossil Sites
Marine molluscs related to modern day squid, octopus, and pearly nautilus, belemnites were present on the Earth for a period spanning over 140 million years and disappeared about the same time of the dinosaur mass extinction approximately 65 million years ago at the end of the Cretaceous Period.
Built for speed, belemnites are believed to have been efficient carnivores that caught small fish and other marine animals with ten hooked tentacles and which were consumed with their beak-like jaws.
Information from the Delaware Geological Survey
Official State Mineral of Delaware
Delaware recognized sillimanite as the official state mineral in 1977.
Sillimanite is widespread in the metamorphic rocks of the Delaware Piedmont and large masses of sillimanite can be found as stream-rounded boulders at the Brandywine Springs State Park. These mineral boulders are remarkable for their size and purity. Delaware sillimanite has a fibrous wood-like texture and could potentially be cut into non-faceted gems showing a "cat's eye" effect. The Delaware Geological Survey also presents information on collecting sillimanite at the Woodlawn Quarry.