Types OF Rock
Ahmad Sameer Nawab
24 March 2014
Igneous Rocks and it’s types.
Sedimentary Rocks and it’s types.
Metamorphic Rocks and it’s types.
Rock type is usually defined as a particular kind of rock having a
specific set of characteristics.
Rock types are specific assemblages of minerals (most rocks are
composed of minerals).
Rocks are much more vaguely defined than minerals. Even rocks
within one rock type may have a highly variable composition.
Still, there is a fundamentally sound reason to talk about such a vague
concept as a rock type because these assemblages occur again and
again in many different locations.
Rock type is like a biome (desert, savannah, rain forest). One
particular desert may greatly differ from another (one is sandy and
another rocky) but they both share something that is common (low
Exactly the same is true with rock types — one granite may be white
and another red but they both have a similar composition (major
minerals are feldspar and quartz).
Here is a list of major rock types recognized by geologists. Immense
number of rock types have been defined (their definitions often
overlapping) and many rock classifications exist. However, there
seems to be a fair number of terms and classification principles that
have successfully stood the test of time.
It all starts with igneous rocks. The Earth is believed to have been
entirely molten in its early stages of development. Hence, all other rock
types are derivatives of igneous rocks.
Sedimentary rocks are products of the consolidation of loose
sediments which are in most part bits and pieces of other
disintegrated rocks. There are three main types of sedimentary
rocks: mudstone, sandstone, limestone. Sure, this is very simplistic
approach but volumetrically almost all sedimentary rocks fall under
these categories if we give them relatively broad definition e.g.
sandstone also includes siltstones and conglomerates, and limestone
includes all sedimentary carbonate rocks. There are notable
exception that do not fit into this classification scheme like
evaporates, coal, and chert but volumetrically they are clearly less
important. In the list below, of course, these exceptions are not
Metamorphic rocks are derived from other pre-existing rocks by
mineralogical and/or structural changes. Metamorphism takes place
in the solid state and at elevated pressure and temperature
generally at depth in the crust.
1. Jackson, J. A. (1997). Glossary of Geology, 4th Edition.
American Geological Institute.
2. Barth, T. F. W. (2007). Quartzite. In: McGraw Hill Encyclopedia
of Science & Technology, 10th Edition. McGraw-Hill. Volume 14.
3. Tilling, Robert I. (2007). Ignimbrite. In: McGraw Hill
Encyclopedia of Science & Technology, 10th Edition. McGraw-Hill.
Volume 9. 20-21.