EnchantedLearning.com Rock and Mineral Dictionary

Most fossils are excavated from sedimentary rock layers. Sedimentary rock is rock that has formed from sediment, like sand, mud, small pieces of rocks. Over long periods of time, these small pieces of debris are compressed (squeezed) as they are buried under more and more layers of sediment that piles up on top of it. Eventually, they are compressed into sedimentary rock. It is made of strata, or layers. The layers that are farther down in the Earth are older than the top layers.

Most sedimentary rock layers are buried under soil or other rocks. The easiest way to find fossils is to find exposed sedimentary rock outcroppings. Good places to look include cliffs, river banks, road cuts, quarries, and desert badlands where erosion is escalated.

Some types of sedimentary rock include:

• Sandstone - a very grainy rock that comes in many colors, including gray, red, or tan. Under a magnifying glass you can see the grains in the rock clearly. Sandstone formed from desert deposits and from shallow seas.
• Shale - is a dark-colored rock that is usually black, deep red, or gray-green. When shale is wet it get very slippery. It has a fine grain and is usually found below sandstone, not on the surface. Shale was formed from fine silt and clay.
• Limestone - is a white to gray, fine-grained rock. It is made of calcium carbonate. It fizzles when it comes in contact with vinegar or any other acid. Limestone was formed from the remains of ancient seas; it is made mostly of calcite precipitated from living organisms. Coquina is a type of limestone that is mostly made of shells and shell fragment. Dolomite is another type of limestone.

Sedimentary rock layers that were formed in water frequently has ripple marks. Sedimentary rock layers that have crackles from drying mud were formed in shallow water that evaporated. Knowing the environmental conditions at the time the rock was formed tells you a lot about what type of fossils may be within the rock layer.

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