Types OF RockAhmad Sameer Nawab

Engineering GeologyKardan University24 March 2014

Outline

Igneous Rocks and it’s types.

Sedimentary Rocks and it’s types.

Metamorphic Rocks and it’s types.

Rock 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 precipitation).

Rock types

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.

IGNEOUS ROCKS

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.

Types OF Igneous Rock

SEDIMENTARY 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 neglected.

SEDIMENTARY ROCKS

Types Of Sedimentary Rocks

METAMORPHIC ROCKS

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.

Types OF Metamorphic Rocks

References

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. 722.3. Tilling, Robert I. (2007). Ignimbrite. In: McGraw Hill Encyclopedia of Science & Technology, 10th Edition. McGraw-Hill. Volume 9. 20-21.

http://www.sandatlas.org/rock-types/