| 21. | Zonation patterns associated with igneous activity are usually easy to interpret.
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| 22. | Also, potassium-argon dating is used to date igneous rocks.
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| 23. | Tuff can be classified as either sedimentary or igneous rocks.
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| 24. | These minerals are typical weathering products of mafic igneous rocks.
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| 25. | It can be found in igneous rocks containing potassium feldspar and plagioclase.
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| 26. | However both are derived from the alteration of igneous rocks.
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| 27. | The rock is an uncommon mafic igneous rock known as a troctolite.
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| 28. | Granite is an intrusive igneous rock, thus not volcanic.
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| 29. | Two different groups of igneous rock have been found within Alexander Island.
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| 30. | THEMIS found a wide range of igneous rocks and minerals.
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