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Pegmatite is very crystalline, an intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatic. Most pegmatites are composed of quartz, feldspar and mica; in essence a granite.

Igneous rocks formed from lava flows of the Archaean era (>2,700 million years ago) are often found to contain disequilibrium-textured crystals characterized by spherulitic, branching or dendritic morphologies that occur in layers near the flow surface.