This is an Earthcache – as such, there is no physical cache. Instead after examining the remnants of the Freestone Point sandstone quarry at the posted coordinates you will answer 4 questions and message me the answers. This earthcache is located in Leesylvania State Park with permission. All observations of these rocks can be made without climbing up the quarry cliff or walking into the briars. There is one restricted area by the cliffs at the far end of the beach. PLEASE OBEY THE POSTED SIGNS! Rock collecting is forbidden in Virginia State Parks. For more information about hours of operation, parking fees, and park rules please visit this LEESYLVANIA STATE PARK link.
FREESTONE POINT
Locally the area is known as "Freestone Point," referring to the sandstone early settlers took from this location for building. Freestone Point was actively quarried during colonial times. The sandstone was easily cut and transported by boat long the river. The abundant supply of inexpensive building material available at this site led early colonists to perceive it as almost “free stone.” The sandstone quarried from the point was used as the foundation material for the manor house and other buildings of Henry Lee and his wife Lucy Grymes Lee when they settled here and established the Leesylvania Plantation around 1750.
The quarry area has increasingly become more overgrown after this earthcache was placed. There are quite a few big freestone blocks laying around. I have highlighted them in the photo above.
SANDSTONE
Freestone Point is in the Potomac Formation, a period of the late cretaceous era. This formation constitutes the base of the Coastal Plain in the mid-Atlantic region, and extends from southern Virginia to northern New Jersey. Sediments now exposed at the top of the Coastal Plain were never buried deep, so the sand and gravel is only loosely consolidated into rock. The sandstone stone at this quarry is sedimentary rock.
Sedimentary rocks are made when sand, mud and pebbles get laid down in layers. Over time, these layers are squashed under more and more layers. Eventually, the layers are turned to rock, a process called lithification. Sedimentary rocks can be formed in deserts, lakes, rivers and seas. The sediment that makes up sedimentary rocks come from other rocks that have been worn down by wind, rain and snow. Over time these sand particles are compacted by pressure of overlying deposits, and get “glued” together by a process called cementation.
Cementing agents are the materials that hold the sandstone together. The composition of the stone and the cementing agent used will determine the strength, durability and weather-resistant properties of the sandstone. Listed below are these agents:
SILICA CEMENT, also called quartz cement, creates the strongest and most durable type of sandstone used for building. The cement is a result of the quartz grains overgrowing and expanding the crystallized forms until it runs into another quartz crystal. This type of sandstone typically forms in environments that have high-energy currents, such as beaches, marine bars and desert dunes.
CALCITE CEMENT is the most common type of cement found in sandstone. The calcite cement typically forms in patches and does not fill all the gaps within the stone. This makes calcite cement sandstone very porous. Calcite is also soluble in water, which can erode away the cement making the stone even more porous.
IRON OXIDES are another common cementing agent in sandstone, also called hematite cement. The iron present in the cement will give the sandstone a distinctive red color. According to the Stone Care Techniques website, iron oxide cemented sandstone weather well in dry climates and become harder and stronger, resisting weathering and deterioration.
Sandstone also has OTHER CEMENTING AGENTS that occur in less common forms. These cementing agents include pyrite, barite, clay, and gypsum. These cementing agents form crystals between the particles of the stone. These cements produce a much softer type of sandstone with the particles able to be rubbed off the stone with your hand.
LOGGING REQUIREMENTS:
To log this Earthcache: Read the geology lesson above. Answer all four questions posted below and send via e-mail or messenger contacts on my Geocaching profile.
QUESTION 1. What is the process called when sediment layers are turned to rock?
QUESTION 2. Feel the rock. Do the grains feel tightly cemented on or do they rub off easily?
QUESTION 3. In your opinion what type of cement agent do you think this sandstone is glued together by?
QUESTION 4. Would sandstone from Freestone Point be good as a building construction material?
OPTIONAL: POST PHOTO. Posting a photo that readily indicates that you (and anyone else logging the find) are at the location.
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REFERENCES:
1. BEARD, R., Rockhounding Virginia: A Guide to the State’s Best Rockhounding Sites, Pg 56-58, Falcon Guides, 2017, https://books.google.com
2. Circular 1264, U.S. Department of the Interior, Geological Society of America, March 24-27, 2004, Page 9, books.google.com
3. Nelson, Steven A., Sandstones & Conglomerates, Geology 212, Petrology, April 17, 2013, tulane.edu
4. "Once Upon a Time..." (The Story of the Rocks in Northern Virginia), website, virginiaplaces.org
5. At the Point of Rock, Historic Marker, erected by Leesylvania State Park
6. Fontaine, William Morris, The Potomac Formation in Virginia, Department of the Interior, 1896, pg 123pubs.usgs.gov
7. Carpenter, Michael E., What Are the Three Most Common Cementing Agents for Sandstones?, April 24, 2017, sciencing.com