Igneous rock (derived frae the Laitin wird ignis meanin fire) is ane o the three main rock types, the ithers bein sedimentary an metamorphic rock. Igneous rock is furmed through the cuilin an solidification o magma or lava. Igneous rock mey furm wi or wioot crystallization, either belaw the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derivit frae partial melts o pre-existin rocks in either a planet's mantle or crust. Typically, the meltin is caused bi ane or mair o three processes: an increase in temperatur, a decrease in pressur, or a chynge in composeetion. Ower 700 types o igneous rocks hae been describit, maist o them havin furmed beneath the surface o Yird's crust.