SIMPLIFIED ROCK IDENTIFICATION CHARTS
The following rock charts will help you to identify rocks in the lab:
IGNEOUS ROCKS: Igneous rocks have an interlocking appearance. In a rock with phaneritic texture individual mineral grains can been seen. In a gabbro this is difficult but you can see light reflected off cleavage planes. Compare igneous rocks to other types of rocks and you will see the difference.
GLASSY TEXTURE: OBSIDIAN
PUMICE
SCORIA
PORPHYRITIC TEXTURE: Large crystal grains in a fine grained groundmass.
SEDIMENTARY ROCKS:
Sedimentary rocks often feel "gritty" like sandpaper, sometimes visible sediment particles are visible and rocks look like concrete. Compare sedimentary rocks to other types of rocks and you will see the difference, rocks look dull and "earthy".
CLASTIC or DETRITAL
SEDIMENTARY ROCKS: rocks composed of sedimentary fragments
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CONGLOMERATE
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large rounded sediment fragments |
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BRECCIA
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large angular sediment fragments |
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SANDSTONE
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sand sized sediment fragments |
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SHALE
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silt and clay sized particles |
BIOCLASTIC SEDIMENTARY ROCK: rock composed of remains of once living organisms
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LIMESTONE
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calcium carbonate material from microscopic organisms |
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FOSSILIFEROUS LIMESTONE
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large fossils easily visible in rock |
METAMORPHIC ROCKS
All metamorphic rocks have either banding or a distinct "sheen" to them, look at the rock and if it seems to have a sheen it is probably a metamorphic rock. Compare metamorphic rocks to other rock types and you will see what this means.
FOLIATED: Mineral grains within the rock are aligned parallel to each other.
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GNEISS
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visible banding |
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SCHIST
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foliation is expressed as "flaky" appearance |
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SLATE
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foliation is expressed as rock cleavage |
NONFOLIATED: No parallel alignment of mineral grains.
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QUARTZITE
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rock composed of silicate material, wide range of colors |
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MARBLE
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rock composed of carbonate material, wide range of colors
identified using acid test |
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