Mainly there are three types of rocks namely, igneous rock, sedimentary rock, and metamorphic rock.
Rock or the bedrock is very important in civil and structural engineering designs. Even for a shallow foundation if we can find the rock to place the foundation, that would be great. However, we can not expect the same everywhere.
In deep foundations such as cast in situ pile construction, the pile is rested on the bedrock having the good condition to bear the applied load.
Therefore, it is very important for structural engineers also to be aware of the type of rock available in the world.
Sedimentary Rock
Sedimentary rocks are formed by the accumulation or deposition of mineral or organic particles. This formation occurs by compaction and cementation.
Further, these types of rocks are formed from pieces of reck accumulation too.
Sedimentary rocks are formed near the earth’s surface, not like igneous rock and metamorphic rock.
The coverage of the sedimentary rock of earth crust is about 73% of the earth’s current land surface. However, the total volume of the sedimentary rock is about 8% of the volume of the crust.
Sedimentary rocks are the types of rocks that cover the earth’s crust as a thin layer and igneous rock and metamorphic rock are cover the rest of the rock volume.
Igneous Rock
Igneous rocks are formed from cooling magma and it is also called magmatic rocks.
The rate of cooling and cooling methods significantly affect the formation of igneous rock types.
Igneous rock covers the earth’s crust by about 15% surface area. Most of the ocean’s crust is covered by igneous rocks.
Metamorphic Rock
Metamorphic rocks are formed when the minerals in an existing rock are changed by heat or pressure within the earth.
In other words, metamorphic rocks are types of rocks formed from igneous rocks and sedimentary rocks. Further, it can be stated as the transformation of existing rock to new types of rocks in the process of metamorphism.
Metamorphic rock is the larger part of the rock and has about 12% of the earth’s crust.
The following table indicates the types of rocks that are included under each category.
| Sedimentary Rock | Igneous Rock | Metamorphic Rock |
| Glacial conglomerate | Granite | Gneiss |
| Shale | Kimberlite | Slate |
| Sand Stone | Lherzolitic with basalt crust | Schist |
| Chalk | Gabbro | Jadeite |
| Shelly Limestone | Basalt | Garnet Amphibolite |
| Anthracite | Rhyolite | Marble |
| Banded Iran | Obsidian | Deformed Conglomerate |
| Pegmatite | Sphalerite Ore Rock | |
| Pumice | Eclogite | |
| Dacite |