Rocks at Your Feet
If you stop by the Nelson County Visitor Information Center and the Nelson County Library, you also have an opportunity to learn about the underlying geology of Nelson County by checking out the nearby exhibit, which includes a sample of nelsonite.
Formation
Nelsonite is a plutonic or igneous rock that formed by the slow cooling of magma beneath the earth’s surface over one billion years ago. Nelsonite is primarily composed of the minerals ilmenite and apatite. It was economically important to Nelson County in the 20th century as it was mined for titanium dioxide. However, it is no longer mined in the area.
Rock of the Year (2016)
In 2016, the Virginia state legislature designated Nelsonite as the state (commonwealth?) rock of Virginia. Nelsonite was named by Thomas L. Watson, a former Virginia state geologist who first discovered the mineral in Nelson County.
Outdoor Rock Concert
Outside of the Nelson County Visitor Center is the Keith Frye Memorial Rock Exhibit, which contains more than two dozen examples of the rocks and minerals that form the foundation of the commonwealth of Virginia. Each sample is identified by name and includes references to geological era and formation. Included in the collection is an example of nelsonite. In addition to checking out the rock samples, spend some time on the information sign, which contains three key topics:
- Celebrating the Geology of Nelson County, Virginia - which classifies the rock samples by their age. Rocks in the exhibit range in age from the Mesozoic back to the Middle Proterozoic periods.
- Nelson County Rock Families - This diagram provides insights to the locations of the rock samples prior to the formation of the Blue Ridge mountain range, which is actually the result of the folding of an arch (Blue Ridge anticlinorium).
- A Cartoon Excursion Through Time: Tectonic Evolution of Nelson County - While cartoons provide the artwork, the descriptions are all serious. Six stages in the life of mountain formation in the area provides insights about how these rocks ended up where they are today (before becoming samples in the exhibit).
Logging Requirements
Either by messaging through the site or sending an e-mail to the cache owner, please submit your responses to the following questions. While you can log your find prior to receiving confirmation, the cache owner reserves the right to delete logs that are not supported by a message with good responses.
- Refer to "Celebrating the Geology of Nelson County." What are the three types of Middle Proterozoic crystalline rocks and to which one does nelsonite belong?
- Refer to "Nelson County Rock Families." What are the Middle Proterozoic (pre-Grenville) gneisses (3) and what place name is associated with them?
- Refer to "A Cartoon Excursion Through Time: Tectonic Evolution of Nelson County."
a) What rose upward to ultimately become the Blue Ridge?
b) Why is nelsonite not referenced on this portion of the sign?
- Describe the size, color, and texture of the nelsonite sample (#6) in the exhibit. Feel free to include in your log a photo of you and/or your GPS with the nelsonite example (which is not at the sign.)
Permission
Permission has been granted by the Director of the Nelson County Visitors Information Center to place this Earthcache.
References
- A Virginia Rockhounder's Web Site Keith Frye Memorial Rock Exhibit
- Virginia Division of Geology Rocks of Virginia