Rocks and Minerals

All of these rocks and minerals are found inside the borders of Frederick County. Many of them may be found at your school or in your neighborhood.

Diabase

igneous rock, green-tan (salt and pepper texture), used for crushed stone or gravel, magma cooled in the geosphere, very difficult to break

Shale

“Gettysburg Shale” : sedimentary rock, red, used to make bricks, formed by interaction of the hydrosphere and geosphere

Hornfels

metamorphic rock, grayish black, was once shale changed due contact metamorphism in the geosphere

Quartz

mineral (7.5-8.5 hardness), glassy white to smoky grey, it is the second most abundant mineral in the Earth's continental crust

Limonite

“Iron Ore”: mineral (5.5 hardness), brown rusting, 70% iron 30% other materials, can be used to make iron products

Greenstone

“Catoctin Meta-Basalt”: metamorphic rock, green, crushed greenstone can be used for shingles and tennis courts

Metarhyolite

Metarhyolite “Blue Flint”: metamorphic rock, dark gray-blue, breaks in sharp edges, Native Americans used this rock to make tools and points

Quartzite

“Meta-Sandstone”: metamorphic rock, grayish-white, once sea-bottom sandstone changed to quartzite with appalachian uplifted

Conglomerate

sedimentary rock, mixture of sandstone, limestone, and the mineral calcite give this rock its red, grey and white color, use to make pillars in the U.S. Capital Building, formed by the hydrosphere and geosphere

Limestone

sedimentary rock, light grey (Grove Limestone) to dark blue (Frederik Limestone), used for burnt lime, gravel, cement and building materials, usually skeletal remains of marine organisms, formed by hydrosphere and biosphere

Calcite

calcium carbonate: mineral (3 hardness), milky white to pinkish red, it is the major mineral in limestone, makes up bones, shells, coral, limestone, marble, and chalk

Sandstone

sedimentary rock, reddish color, once sea-bottom sand, iron impurities cause red color, formed by hydrosphere and geosphere

These are some of the most common rocks and minerals in the county. Many of them can be found outside your school and in your neighborhood.