Delaware is a coastal-plain state with almost no hard rock, so its state mineral comes from the one corner that has any: the Piedmont hills above Wilmington, where sillimanite occurs in the old metamorphic rock. Local tribes quarried the tough massive form of it for tools long before the state existed. There is no fee dig here and much of the ground is PRIVATE or park land where collecting is not allowed, so treat this as a geology stop rather than a dig, and see the specimens at the Delaware Mineralogical Society and the university collections.
Sillimanite
See it on the map
Other places on the map within a couple of hours.
