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Comment: 07:53 - 08:44 (00:51)
Source: Annenberg/CPB Resources - Earth Revealed - 14. Intrusive Igneous Rocks
Keywords: crystal, "J. Lawford Anderson", "igneous rock", mineral, magma, plagioclase, olivine, potassium, feldspar, quartz
Our transcription: By studying the crystal textures of igneous rocks, geologists have discovered that not all minerals form from a magma at the same time and temperature.
Rather magma crystallizes one or two mineral types at a time.
The early forming crystals, those that could withstand higher temperatures, such as plagioclase or olivine preserve symmetrical shapes that could only have resulted from the crystal formation taking place in a liquid.
Later forming crystals, such as potassium feldspar and quartz exhibit irregular shapes indicating that they crystallized last from small compartments of liquid confined in the spaces remaining between the early forming crystals.
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