Читать книгу Engineering Physics of High-Temperature Materials - Nirmal K. Sinha - Страница 68

Rocks formed due to the solidification of lava or magma on or below Earth's surface are called igneous rocks. Since the solidification of molten rocks depends upon the mode of cooling and the rate of heat transfer, texture (size, shape, and arrangements of grains) and mineral composition of igneous rocks depend on the place of cooling. Extruded lava and flowing lava are subjected to rapid cooling rates and tend to produce fine‐grained and relatively homogeneous materials. The size and shape of the grain and the mineral composition of solidified magma depend on the depth below Earth's surface due primarily to decrease in the cooling rate with increase in depth. The cross‐sectional grain sizes increase with decrease in the rate of solidification, and hence increase in depth. For convenience, igneous rocks are divided into three basic types: extrusive (or volcanic), hypabyssal, and intrusive (or plutonic). Extrusive igneous rocks are fine grained, and intrusive igneous rocks are very coarse grained. Granite, diorite, and gabbro are examples of coarse‐grained intrusive type of igneous rocks.