How to Identify Types of Rocks
The key to identifying rocks is first to identify the minerals that compose them. Geologists and students should begin with the most obvious type of rock. Follow these steps to help you identify types of rocks using a number of methods.
- Difficulty:
- Challenging
Instructions
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Look at your rock to see if it has a metallic or non-metallic luster. Common metallic minerals include sulfides, oxides or a metallic element.
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Determine your rock's density. Most rocks with a metallic luster also are high in density. Few non-metallic minerals have high density. Barite and sphalerite are the most common high density non-metallic minerals.
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Inspect your rock for its degree of hardness. If you can scratch glass with your rock, and it's metallic, consider oxides. If it's non-metallic and scratches glass, suspect such common minerals as quartz, feldspar or a silicate. If you can scratch your rock easily with a knife, suspect common sulfates, carbonates or halides.
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4
Examine your rock for its particular cleavage. Of the many different types of cleavage, common properties include cubic, octahedral, rhombohedral, blocky cleavage, thin sheets or splintery cleavage.
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Determine the color of your rock. Color is the least reliable of identifying properties, as stains or impurities can compromise a rock's true color. Pink can indicate feldspars, silicates or carbonates. Bright yellow, red or orange can indicate sulfides, oxides, uranium, chromate. Earth tones can indicate iron and bright green to blue can show coppers.
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Tips & Warnings
There are a number of other tests to further distinguish specific rock specimens, including testing for acid or vinegar fizz, looking for crystals and how they're arranged, searching for holes or porous materials, and examining the surface for glassy or dull properties. Use these tests along with a detailed rock identification guide.
