Intrusive igneous rocks are those that form from the solidification of a magma below the earth's surface. The size and shape of an intrusion, or body of solidified magma, is dictated by numerous factors. Geologists give different names to igneous intrusions that are based on the depth of emplacement, the specific orientational relationship to the surrounding host rocks, and the shape and size of the intrusion. Such names as dike, sill, volcanic plug, and many others are used to describe these features. As seen below, diatremes are a special type of igneous intrusion.
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