Magma Types and Igneous Rock Classification
Magma: Composition and Types
Magma is molten rock. It is composed of fused silicates, although it may contain other molten materials such as oxides, sulfides, or sulfates in very low proportions. Magma is distinguished into three types:
- Basaltic (Basic) Magma: The most fluid and abundant type. It is produced by the partial melting of mantle material. It melts at higher temperatures, has a higher density, and consists of Fe, Mg, and Ca silicates.
- Andesitic (Intermediate) Magma: The least abundant type, produced by the partial melting of oceanic crust.
- Granitic (Acid) Magma: The most viscous type. It melts at lower temperatures, and the melting occurs from the continental crust. It is lighter and composed of Na, Ca, K, and Fe silicates.
Igneous Rocks
Igneous rocks are formed by silicate minerals, which are the most common and frequent minerals in both the Earth's crust and mantle. The most abundant silicate groups are:
- Quartz: A tectosilicate formed by SiO2, found in many rocks.
- Feldspar: Tectosilicates of aluminum with K, such as potassium feldspar (orthoclase) or plagioclase.
- Micas: Such as black mica (biotite) or white mica (muscovite).
- Amphiboles: Inosilicates with a double chain of varied composition.
- Pyroxenes: Inosilicates with a simple chain formed by Ca, Mg, and Fe silicates, typically dark in color.
- Olivine: A nesosilicate of Fe and Mg. It is a ferromagnesian mineral formed at high temperatures.
Main Magmatic Rocks
These can be divided into three groups:
Plutonic Rocks
These rocks crystallize inside the Earth slowly, resulting in a medium to coarse-grained texture. Examples include: Sienite, Granite, Granodiorite, Diorite, Gabbro, and Peridotite.
Volcanic Rocks
These crystallize on the surface very quickly, meaning atoms do not have time to organize. Examples include: Rhyolite, Trachyte, Basalt, Andesite, Obsidian, and Pumice.
Filonian (Hypabyssal) Rocks
These originate from relatively rapid cooling of magma in areas near the surface, showing characteristics midway between plutonic and volcanic rocks. Examples include: Aplite, Diabase, and Porphyry.