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Igneous rock - Wikipedia, the free encyclopedia (1589 words) |
 | In a simplified classification, igneous rock types are separated on the basis of the type of feldspar present, the presence or absence of quartz, and in rocks with no feldspar or quartz, the type of iron or magnesium minerals present. |
| The most important distinction in igneous rocks is texture, which is the physical character of the rock, including the size, shape, orientation, and distribution of grains and the intergrain relationships. |
| Porphyritic textures are an intermediate situation between the previous two: the groundmass of the rock has an aphanitic texture, but crystals (termed in this particular occurrence as phenocrysts) are visible to unaided eye. |
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