How to Identify Rocks
According to The Department of the Glendale Community College, rocks are naturally occurring combination of minerals, soil and fossil materials. Rocks are identified as igneous, sedimentary or metaphoric. According to the University of Wisconsin, you cannot identify a rock without first knowing its composition. One of the most popular ways to determine a rock's composition is to make basic assumptions and then eliminate certain classifications based on its texture, origin and color.
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Instructions
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Take educated guesses on the makeup of the rock. Check for the common makeup first---sulfur---by sniffing for a sulfuric or rotten egg odor. If the rock can scratch glass, suspect that it is silicate, unless it is metallic in luster. In that case, the rock should be identified as having an oxide composition. According to the University of Wisconsin-Green Bay's "Identifying Rocks and Minerals," soft non-metallic minerals that can be scratched with a knife are made up of carbonates, halides or sulfates.
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Feel the texture of each rock to determine its origin. Verify whether it has a frothy or fine-grained texture. If it has either, classify the rock as either igneous or a derivation from volcanic ashes or molt. If the rock's grains are loosened from weathering, the rock could have originated from large rock structures. These are considered igneous platonic. Run your hands over rocks that appear smooth---these rocks can be classified as sedimentary rocks, or rocks originating from fossil forms. Rocks that have fine textures and obvious bands and streaks are metamorphic rocks.
Sedimentary rocks are discovered when the ocean or other bodies of water carry them to shore. Igneous rocks come from volcanic structures that have spewed forth molten lava and have dried solid. Metaphoric rocks are located at the base of mountains and other rocky geographic landscapes---fault lines---after the movement of the earth's crust has pushed them up to the surface.
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The color of the rock also gives you clues about its composition. The rock should be of copper material if it is green or blue. Green rocks are almost always considered epidotic, or having a high iron silicate concentration. Black to dark green rocks are mostly ferromagnesian---or rocks with high iron and magnesium levels.
Examine a rock's hues. Classify light blue rocks as celestite and those with long crystals as metamorphic. Classify bright hue rocks that are yellow, orange or red as non-metallic sulfides. Yellow-greenish rocks should be classified as uranium minerals.
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References
- Photo Credit colorful tumbled stones image by Tom Oliveira from Fotolia.com
