Gone Outdoors

How to Identify Stones

by Kelly Townsend

Whether you are an avid rock collector or simply interested in finding out how to tell rocks apart, learning to identify the differences between each type of rock usually takes a bit of hard work and practice. This list of steps that will help you determine the best way to find and categorize your stones.

Clean your finds by brushing away obvious debris. For heavily soiled stones, wash with a mild soap and water to eliminate any undesired elements that would prevent you from being able to accurately identify the type of rock. Do not scrub too hard, as you may damage the rock's surface. If the rock is porous, do not soak it in water.

Separate your stones into three categories - igneous, sedimentary or metamorphic. Igneous stones don't have much layering or texture and are usually white, black or grey. Sedimentary stones are hardened layers and primarily brown. Metaphoric rocks are usually light in color and feature shiny layers. In a notebook or ledger, make note of the category for each stone.

Examine each rock carefully and take note of the color, texture, holes and other characteristics. Write down the date and place where you found each rock, along with its defining characteristics.

Pour a very small amount of vinegar on the stone. If the rock bubbles, it may likely be limestone or marble. If it's yellow in color, it's likely to be sulfur. These are very basic tests and can help you identify only a limited number of stones.

Put the stone through a variety of identification tests. To identify stones, you must gather information about each stone, including its luster and hardness. The luster of a stone refers to its ability to reflect light. Luster is categorized as either metallic or non-metallic. If it is metallic, the surface will shine like metal. If it's non-metallic, it will have a dull surface.

Write down whether the stone is metallic or non-metallic and also note its color. The next test is for hardness. Hardness doesn't refer to what it takes to break the stone, but rather what it takes to scratch it. According to GeoMan's Field Hardness Test, you can estimate the hardness scale of a stone by determining what item can scratch it.

Determine the hardness of your stones. If a stone can be scratched with a fingernail, the hardness is approximately 2.5. If it can be scratched wtih a penny, it's 3.5. If it takes a knife blade, it's 4.5. Lastly, if glass can scratch the stone it's 5.5 on the hardness scale. Mark down the hardness number in your ledger.

Find rock identification tables online or at your local bookstore. Using the characteristics you noted in your ledger, you can make a comparison to the identification tables for category, color, luster, hardness and location to determine which type of stones you have found.

Items you will need
  • Wash cloth
  • Soap
  • Vinegar

Photo Credits

  • Flickr: http://flickr.com/photos/chatiryworld/51130213/