Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive ...

In Yellowstone, the Hellroaring and Crevice plutons — large coherent bodies of intrusive rock — are ... out for coarse-grained crystalline igneous rocks —you may just be looking at a rock ...