This Earthcache is an examination of rocks found on this property. I moved them to the edge of the road (with the property owner’s permission) for greater ease of access. You can park next to the cache.
Intro
The great thing about geology is it’s all around you wherever you go. This Earthcache won’t lead you to a spectacular outcrop or overlook, but it does emphasize the point that even in unexpected places you can get a sense of the Earth and its history. If you’re from around Chattanooga, you may have some of these rocks in your own yard.
The Rock Cycle
There are three basic types of rock--igneous, sedimentary, and metamorphic. The Rock Cycle says each type can turn into any of the others given the right conditions and enough time.
Igneous rocks, by definition, form directly from the hardening of molten rock (magma or lava). When exposed to weathering and erosion, igneous rocks break down into sediment, which after being buried by other sediment can harden into sedimentary rocks. If the rocks are subjected to a lot of pressure and/or heat, they can transform into metamorphic rocks. If the heat is great enough, the rocks can re-melt and then turn back into igneous rock if hardening occurs.
Focus on Sedimentary Rocks
Sedimentary rocks come in two broad categories--clastic and non-clastic rocks. Clastic sedimentary rocks (e.g. - conglomerate, breccia, sandstone, shale) are composed of fragments of other rocks (clasts) that have been cemented back together. Non-clastic sedimentary rocks form from the accumulation of organic sediments like shells of sea organisms (e.g. - limestone) or dead plants (e.g. - coal) or from the evaporation of water leaving behind minerals (e.g. - halite, or salt) that were dissolved in the water.
Simple Identification Guide to Some Common Sedimentary Rocks in the Chattanooga Area
Conglomerate - Conglomerate is composed of round pebbles usually surrounded by quartz sand. Often tan colored in this area.
Breccia - Made of angular (jagged) pebbles. Resembles a mosaic artwork. It can be a variety of colors depending on what the angular fragments are composed of and what material cements those fragments.
Sandstone - Composed of quartz sand. On a freshly broken surface, sandstone is often tan colored to reddish.
Shale - You can usually leave a groove with your fingernail in shale because shale has a high clay content. It is often gray to tan.
Limestone - Often gray but you won’t be able to leave a groove in it with your fingernail. Often, too, you can see fossils in limestone, but the fossils can also be microscopic. Because limestone is composed of the mineral calcite, it will fizz if you put some hydrochloric acid on it (in case you happen to carry around hydrochloric acid).
Chert - Often white in this area, chert can also be gray and even black (as flint). Because chert is composed of a type of quartz, it can scratch glass.
Coal - Coal is often black because of its high content of organic matter.
Geologic Info About the Chattanooga Area from the “Rockd” Phone App
The Chattanooga area is part of the Valley and Ridge geologic province located between the Cumberland Plateau to the west and the Appalachian Mountains to the east.
“The Valley and Ridge landscape reflects the remnants of an ancient fold-and-thrust belt, west of the mountain core that formed the Alleghenian orogeny. Here, strata have been folded westward, and forced over massive thrust faults; there is little metamorphism, and no igneous intrusion. The ridges represent the edges of the erosion-resistant strata, and the valleys portray the absence of the more erodible strata.”
(Rockd app: citing Fenneman, N.M, D.W. Johnson, 1946, Physiographic divisions of the conterminous U.S.: USGS.)
The rocks in the Hixson area are from the Cambrian to Ordovician Periods, which puts them at roughly 498-470 million years old.
Location of today’s continents and of Hixson 490 million years ago. From the Rockd app.
Tasks
As with all Earthcaches, message your answers. Do not post them in your log.
1) At GZ there are three groups of large rocks I hauled down in a wheelbarrow. With your back to the road, the rocks on the left are A, in the middle are B, and on the right are C. Use the descriptions above to identify A, B, and C.
2) Rock A is clearly composed of pieces of another sedimentary rock. What rock are the pieces made of? Why do you say that?
3) If you took any of the three rocks and subjected it to a lot of pressure, which general type of rock would you end up with?
4) Optional: Post a photo of yourself with the rocks. Bonus point if you look excited to be there.
5) Optional: There is a traditional cache (PMO) close to this Earthcache. If you feel like going for it, it should be an easy one.