Pliocene
chesapecten jeffersonius
Virginia has no official rock or gemstone. You might consider listing the official fossil which is Chesapecten jeffersonius which was given official status in 1993 by the legislature.
Virginia doesn't have a state dinosaur, and its state fossil is a scallop called Chesapecten jeffersonius. However, birds are dinosaurs, so if you count the state bird, the state dinosaur is the cardinal.
Antebellum Era
Yes. The first era was the precambrian era followed by the paleozoic era then the mesozoic era than the Cenozoic era.
1850 - 1920
Simple. There is no state rock of Virginia. A state fossil, yes (the fossil scallop, Chesapecten). A state rock, alas, no.
no but it might happen in the futurre
Colonial
200 b.C.
the formation of the ozone layer. [apex]
Yes.