A Field Guide to the Identification of Pebbles

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Most common pebbles can be easily identified if you remember a few common tricks used by amateur geologists and rockhounds. These simple methods will help you identify the pebble you picked up or kicked across the street.

Common Sedimentary Rocks

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Sedimentary rocks form, over long periods of time, from materials deposited by wind or water action. Common sedimentary rocks include limestone, sandstone and flint, among others. Shale produces flat, sheet-like rocks with jagged edges. Limestone fizzes in contact with vinegar. Sandstone has a grainy texture, and may leave grains in your hand.

Common Metamorphic Rocks

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Metamorphic rocks form when heat and pressure, over long time periods, cause chemical changes to other types of rock. Common metamorphic rocks include gneiss, marble and quartzite. Gneiss is grey or brown -- sometimes with coloured streaks -- and often breaks into blocks. Marble is usually white with dark streaks. Quartzite has a glassy, crystalline appearance.

Common Igneous Rocks

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Igneous rocks form through volcanic action. Common igneous rocks include granite, basalt and pumice. Pumice is crumbly and glasslike and may float on water. Granite is a hard grey, yellow or pink material containing large quartz crystals. Basalt is dark, heavy and fine-grained, and has various colours.

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