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The rocks and minerals of our area show amazing changes. Check out the photos below of places where you can find all these rocks and minerals.
Rocky Ridge Samples
Shale - The Gettysburg Shale in our area is a red sedimentary rock. It breaks apart easily. It was formed through interactions between the hydrosphere and geosphere.
Hornfels - Hornfels is a grayish, blackish, or sometimes purple metamorphic rock. This rock was changed within the geosphere. Millions of years ago it was shale.
Diabase - Diabase is an igneous rock found along Rocky Ridge. When weathered it can look green or tan. However, when broken open it reveals small "salt and pepper" crystals that appear as different shades of black and white. This rock was magma long ago that cooled in the geosphere. It can also be difficult to break.
South Mountain and Catoctin Mountain Samples
Limonite - Limonite is a mineral found at the base of the mountains in and around Frederick. It's easily identified by the rusty orange colors, indicative of iron. At times it will even appear to have holes in it. It was formed within the geosphere.
Greenstone - This green metamorphic rock was once an oceanic basalt that was formed in the hydrosphere and changed, or metamorphosed, and pushed up by forces inside the geosphere (Earth).
Rhyolite - Often identified by its grayish color and sharp edges, rhyolite is a metamorphic rock that can be found in a few areas in the mountains of Frederick County. Rhyolite was formed by cooled lava under the oceans millions of years ago. It was pushed upwards and changed in the geosphere.
Quartzite - Quartzite is a hard metamorphic rock that was once crystals of sand. It was compressed at the bottom of the ocean millions of years ago, then pushed up in the geosphere. Now you can find it at higher elevations in Frederick County because it resists weathering more than the rocks that were once above it. Click here to read more about this rock in our county at Sugarloaf Mountain and Devil's Racecourse.
Southern Frederick County Samples
Quartz - Quartz is a clearish white mineral found in Frederick County. It is also the most common mineral is the world. It was formed within the hydrosphere and geosphere.
Conglomerate - Conglomerate is a sedimentary mixture of limestone and sandstone that is held together by calcite. It was formed between interactions with the hydrosphere and geosphere. Easily identified by its multiple colors.
Calcite - This milky white mineral is considered soft (when compared to other minerals). Look for a color that is more opaque. It may also have traces of iron or other impurities. Calcite can be found in limstone and conglomerate. It was formed between interactions between the hydrosphere, biosphere, and geosphere.
Limestone - The most common rock in the Frederick Valley, limestone can be identified by its gray color. This sedimentary rock is used throughout the county for many uses. It was formed under water in the hydrosphere and made from organisms in the biosphere.
Sandstone - Sandstone is a sedimentary rock comprised of many grains of sand that have been pressed together over tremendous pressure under an ancient ocean. It was formed in the geosphere and hydrosphere. Locally you can also identify it by its reddish color.
Fifth grade students in Frederick County participate in a two day study of the Earth's Systems. Student study the rocks and minerals of our county as they relate to the spheres of the Earth: biosphere, hydrosphere, atmosphere, and the geosphere. We typically collect geologic samples in three locations: Rocky Ridge, Catoctin and South Mountain, and Southern Frederick County. Students use a dichotomous key to help identify their samples at school, after their field experience.
Outdoor School Rock and Mineral Key for Earth Systems.pdf