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A Field Guide to the Identification of Pebbles

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

Common Sedimentary Rocks
- Limestone is a common sedimentary rock.
  
  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
- Quartz is Earth's most common rock.
  
  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 gray or brown -- sometimes with colored streaks -- and often breaks into blocks. Marble is usually white with dark streaks. Quartzite has a glassy, crystalline appearance.
Common Igneous Rocks
- The grain pattern on these blocks identifies them as granite.
  
  Igneous rocks form through volcanic action. Common igneous rocks include granite, basalt and pumice. Pumice is crumbly and glass-like and may float on water. Granite is a hard gray, yellow or pink material containing large quartz crystals. Basalt is dark, heavy and fine-grained, and has various colors.

Rocks & Minerals