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Igneous Rocks
Rocks formed through the cooling and solidification of magma or lava.
Sedimentary Rocks
Rocks formed by the accumulation and compaction of mineral and organic particles.
Metamorphic Rocks
Rocks that have been transformed by heat, pressure, or chemically active fluids.
Decompression Melting
Melting that occurs when pressure drops on hot rock, leading to the formation of magma.
Partial Melting
The process by which only a portion of a solid melts to form magma.
Lava
Molten rock that erupts onto the Earth's surface.
Mafic magma
Formed by melting mantle - igneous rock that is rich in magnesium and iron - dark in color - BASALTIC.
Intermediate magma
Formed by melting continential crust - Igneous rock that has a medium amount of magnesium, iron, and silica - moderate light color (kinda dark, kinda light) - ANDESITIC.
Felsic magma
Igneous rocks that are rich in silica - light in color - more viscous than mafic magma - GRANITIC.
Assimilation
The process by which solid or fluid foreign material is incorporated into magma - can change the magma chemistry.
Mixing
Two magmas combine on their way to the surface.
Phaneritic
A texture of igneous rocks where crystals are large enough to be seen with the unaided eye - slow crystallization inside crust.
Aphanitic
A texture of igneous rocks where crystals are too small to be seen without a microscope or hand lens - “fine-grained” - fast crystallization at the surface.
Porphyritic
A texture characterized by large crystals (phenocrysts) embedded in a finer-grained matrix - mixed coarse & fine-grained material - indicates two phases of crystallization.
Phenocrysts
Large crystals found in a porphyritic igneous rock.
Matrix/Groundmass
Small crystals found in a porphyritic rock that surrounds the larger phenocrysts.
Glassy Texture
A texture of igneous rocks where the rock appears shiny and glass-like due to rapid cooling (ex:Obsidian).
Vesicular Texture
A texture of igneous rocks characterized by the presence of gas bubbles, creating a sponge-like structure (ex: Basalt, Pumice, & Scoria).
Plutonic Rocks
Rocks formed below the Earth’s surface - AKA: Intrusive.
Volcanic Rocks
Rocks formed at the Earth’s surface - AKA: Extrusive.
➢ Basics of the rock cycle:
The rock cycle is a continuous process of formation, alteration, and destruction of rocks, involving igneous, sedimentary, and metamorphic processes.
➢ How igneous rocks form:
Igneous rocks form from the cooling of magma or lava; ions slow down, attract, and begin mineral formation.Then they can be classified into two main types: intrusive and extrusive, depending on their formation location.
➢ Magma vs. Lava:
Magma is found beneath the Earth's crust, while Lava erupts onto the surface during volcanic activity.
~ Magma is molten rock and dissolved gas, forming from either decompression or partial melting. Lava is molten rock material from which gas has mostly escaped.
➢ How rocks melt and why:
Rocks melt due to increased temperature and pressure conditions, often enhanced by the presence of water or other volatiles that lower the melting point of minerals.
***Adding water lowers the melting temperature of rocks.
➢ Types of melting at different plate boundaries:
~ Decompression melting at ocean ridges.
~ Partial melting of subducting slabs.
*Divergent boundary: Decompression melting
*Convergent boundary: Partial melting
➢ How is water added to rocks to lower melting temperature?
Adding water lowers melting temperature of
➢ How can magma chemistry be changed to allow for various rock types from a single magma chamber?
Magma Differentiation allows for the magma chemistry to change through processes such as crystalization, mixing, and assimilation.
➢ Bowen’s Reaction Series:
A concept that explains the order of crystallization of minerals from cooling magma.
➢ Xenoliths:
A piece of rock trapped in another type of rock - usually the rock is embedded in magma while the magma was cooling. These rocks give clues to underlying geology. (ex: Diamonds).
➢ Igneous textures and what they indicate:
Refers to the size, shape, and arrangement of minerals within the rocks, which can indicate the cooling rate and environment of formation. Textures include: Phaneritic, Aphanitic, and Porphyritic.
➢ Plutonic vs. Volcanic Rocks:
Plutonic: (intrusive) formed below Earth’s surface.
Volcanic: (extrusive) formed at the surface.
➢ Batholiths, Sills, & Dikes:
Refers to the types of plutonic structures
Batholiths: large masses formed in Earth’s crust.
Sills: sheet-like intrusions
Dikes: large slab of rock that cuts across layers.
➢ Related igneous rocks (ex: Gabbro and Basalt):
Gabbro: a coarse-grained plutonic rock.
Basalt: a fine-grained volcanic rock.