In the formation in front of you, you should be able to detect a thin line that runs horizontally and that is drastically different to the surrounding layers. This layer is distinct and important to the region. Based on the information below you job is to determine what type of rock you are looking at.
| SANDSTONE (sand'-stone) |
| What Type of Rock Is It? Sedimentary
What Does It Look Like? Sandstone is often red to brown, light gray to nearly white. Sometimes it is yellow or green. It usually is composed of rounded grains that are all of the same size; and it is usually medium grained. Some sandstones show slight color variations in layering.
What Minerals Make Up the Rock? quartz; Sometimes contains: feldspars, mica, glauconite (in green colored sandstone), magnetite, garnet, rutile, ilmenite
How Was It Formed? quartz sand that is produced by the weathering of other rocks (such as granite, gneiss, and other sandstones) is deposited by rivers, waves, or wind. The sediment may have been a sand bar, an ocean beach, or desert sand dunes. The sand is buried under other sediments, compacted by the weight of those sediments, and cemented by material dissolved in water that seeps through it.
Related Rocks: Arkose: Usually red or pink, may be gray. Grains are angular. Arkose contains more than 25% feldspar with quartz. Medium to coarse grained. Greywacke: Black or dark green. Usually contains coarse angular grains included with fine grains.
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| SHALE (sh-ale) |
| What Type of Rock Is It? Sedimentary
What Does It Look Like? Shale may be black, gray, red, brown, dark green, or blue. It is fine grained, so particles usually can not be seen. When moistened, shale usually smells like wet mud. What Minerals Make Up the Rock? clay minerals; Sometimes with some quartz sand, pyrite, gypsum
How Was It Formed? Clay sediments settle in quiet lakes, lagoons, bays, or off-shore areas. When buried and compacted the clays become shale. Iron oxides often help to cement the particles together.
Compare To: slate schist
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| LIMESTONE (lime'-stone) |
| What Type of Rock Is It? Sedimentary
What Does It Look Like? Limestone is usually white, gray, tan, or yellow. It may contain impurities to make it red or black. Fossils are often found in limestone. It may be very smooth or even sugary, fine grained, or medium grained. The powdered rock will usually fizz in white vinegar. Unlike marble, limestone is not composed of visible crystals. What Minerals Make Up the Rock? mostly calcite
How Was It Formed? Most limestone is formed by a chemical reaction in sea water. The reaction makes a lime mud which sinks to the bottom to for the limestone. Some limestones are formed from buried coral reefs.
Related Rocks: Dolostone (doe'-low-stone) looks like limestone, but is composed of the mineral, dolomite. Powdered dolostone does not fizz with white vinegar. Dolostone forms on the ocean floor.
Compare To: marble
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| CONGLOMERATE (cun-glom'-er-at) |
| What Type of Rock Is It? Sedimentary
What Does It Look Like? Conglomerate looks like a mixture of sand and different sizes of rounded pebbles. The pebbles are the important observation.
What Minerals Make Up the Rock? mostly quartz
How Was It Formed? Sand and pebbles collect along sea shores, lake shores, or river banks. They are compacted by the weight of sediments that collect above them and cemented by material dissolved in the water that seeps through them.
Related Rocks: Breccia (brech'-ee-uh) looks like conglomerate, but the "pebbles" in it are jagged and blocky, not rounded.
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Please log your visit and send me an e-mail with the answer to the tasks and questions below.
Please DO NOT put the answers to your questions in the log.
1. Estimate the width of the distinct layer you have observed.
2. What color is the layer and what color are the surrounding layers.
3. Based on the information above, what type of rock is the layer?
4. Post a picture of yourself or a personal item without a spoiler that shows you visited the site. REQUIRED