Metamorphic, Sedimentary, and Igneous Rocks: Types & Formation
Metamorphic Rocks
In some places within the Earth’s interior, rocks are under very high pressures and temperatures, but do not melt. Because of these conditions, the rocks change in texture and composition. These changes are called metamorphism.
Influence of Pressure
Due to the influence of pressure, the holes in the rocks are reduced. If they have crystals, elongated or flattened perpendicular planes are arranged in the dominant pressure direction. This creates sheets, a phenomenon called foliation.
Influence of Temperature
High temperatures can cause significant changes in rocks, such as:
- Loss of water
- Modification of texture, degree of cohesion, and heat
- Transformations of the minerals that form the rock
Texture of Metamorphic Rocks
Metamorphic rocks have several textures:
Texture with Foliation
On spindle or elongated crystals, three types of textures are distinguished: slate, schist, and gneissic.
Texture Without Foliation
These rocks do not have elongated or laminated crystals; crystals are equal in all directions.
Metamorphic Rock Formation
Metamorphic rocks can be formed from any other rock (sedimentary, igneous, or metamorphic) as a result of increased temperature or pressure.
Depending on the composition of the original rock and the pressure and temperature to which it has been subjected, different metamorphic rocks are formed.
The most common metamorphic rocks are: slate, schist, gneiss, marble, and quartzite.
Sedimentary Rocks and Identification
Sedimentary rocks, according to their origin, may be:
Laminated Sedimentary Rocks
Sediment settles to form horizontal layers. As a result of sediment diagenesis, it is transformed into rock, forming a layer.
May contain fossils: the remains of dead organisms deposited with the sediments may be preserved in the rocks as fossils.
Sedimentary rocks are classified as:
Rock Debris
These are formed from solid-state materials transported by entrainment and include conglomerates, sandstones, and argillites.
Non-Debris Rocks
The materials that were transported are dissolved in water or are remnants of organisms, and include limestone, gypsum, halite, peat, lignite, coal, and oil.
Petroleum and coal burn easily and are called fossil fuels.
Igneous Rocks
Igneous rocks are caused by the solidification of magma as lava or pyroclastics.
Igneous rocks are classified as:
- Volcanic rocks: formed by the rapid solidification of magma on the Earth’s surface.
- Plutonic Rocks: formed by slow solidification of magma deep within the Earth.
Based on their degree of crystallization, three types of textures are distinguished: holocrystalline, hypocrystalline, and vitreous.
Volcanic Rocks
These arise when magma cools and solidifies on the Earth’s surface. Volcanic rocks have a glassy or hypocrystalline texture; this texture is called vacuoles.
The volcanic rocks include basalt (most abundant in the Canary Islands), pumice, and obsidian.
Plutonic Rocks
They originate from magma inside the Earth and solidify in magmatic chambers. They have a holocrystalline texture and include granite (the most frequent rock in the Iberian Peninsula), syenites, and gabbros.
Vocabulary
Moderate: To save the environment with specific ends.
Karst: The formation of limestone, produced by the erosive action of water or solvent.
Sedimentary rocks: Limestone, gypsum, halite, peat, lignite, coal, oil, and coal.
Volcanic rocks: Basalt, pumice, obsidian.
Plutonic rocks: Granite, syenite, gabbro.
Metamorphic Rocks: Slate, schist, gneiss, marble, quartzite.