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Igneous Rocks
| Term | Definition |
|---|---|
| Igneous Rocks | Rocks formed through the cooling and crystallization of molten rock; the starting point of the rock cycle |
| Magma | Molten rock beneath the surface; hotter than the surrounding rock and has lower density and migrates upward through bedrock. |
| Lava | Magma erupted at the surface; hot enough to melt. |
| Felsic Rocks | >65% Silica (Si); Abundant in Sodium, Potassium, and Aluminum; Has little calcium, Iron, and Magnesium. |
| Mafic Rocks | <52% Silica (Si); Abundant in Calcium, Iron and Magnesium; Has little Sodium, Potassium and Aluminum. |
| Viscosity | The resistance to flow; Water is low and maple syrup is high in this. |
| Composition | High silica increases viscosity |
| Temperature | increases, viscosity lowers |
| Pressure | lowers, viscosity lowers |
| Dissolved Gases | increases, viscosity lowers |
| Lava Flows | low viscosity |
| Pyroclastic Materials | high viscosity |
| Extrusive Igneous Rocks | Formed by lava at the surface; tend to crystallize rapidly; small crystals form; AKA volcanic rocks |
| Intrusive Igneous Rocks | Formed from magma that cools in the crust; tend to crystallize slowly; larger crystals form; AKA plutonic rocks |
| Igneous textures | Based on the size of the mineral crystals |
| Aphanitic (I.T) | Fine-grained crystals; fast cooling; crystal nucleation is greater than crystal growth |
| Phaneritic (I.T) | Coarse-grained crystals; slow cooling; crystal nucleation is less than crystal growth |
| Porphyritic (I.T) | Variable crystal size; Phenocrysts are larger crystals; Groundmass are finer crystals |
| Pyroclastic (V.T) | Fragmental material; Volcanic ash and bombs; Tuffs and wielded tuffs |
| Glassy (V.T) | No crystals - not a true mineral; Extremely rapidly cooling |
| Vesicular (V.T) | Contains numerous small holes |
| Primary Minerals | Quartz, K Feldspar, Plagioclase Feldspar, Biotite, Hornblende, Pyroxene, Olivine |
| Ultramafic Rocks | Very low Silica Content <45%; Generally green or black; very high density |
| Mafic Rocks | Low Silica content 45%-52%; Usually dark green, grey or black; high density |
| Intermediate Rocks | Moderate Silica content 53%-65%; Wide range of colors; moderate density |
| Felsic Rocks | High silica content >65%; light color; lower density |
| Bowen's Reaction Series | Mafic, Intermediate and Felsic rocks can all arise from the same source magma; Higher melting Temp for the minerals higher on the list and lower melting T for minerals lower on the list; Translates to mineral stability |
| Discontinuous Series | Contains ferromagnesium silicates |
| Continuous Series | Contains only non-ferromagnesium silicates |
| Assimilation | Country Rock- the surrounding rocks in which magma intrudes; Consumed/melted by magma |
| Crystal Settling/Fractional Crystallization | Crystals form and sink to the bottom of the melt because they are more dense, specifically the minerals higher on the Bowen's Reaction Series settle first. |
| Magma Mixing | Different magma may converge into one chamber and mix; mixing of mafic magma with felsic magma would create intermediate magma |
| Spreading Zones | Cracks in the ocean floor where magma breaches and is quenched by ocean water |
| Subduction Zones | Crust is partially melted as it subsides into the mantle; Ocean sediments and Silicon rich continental crust are incorporated into the melt, making the magma more felsic |
| Pyroclastic Flows | Ash and lava fragments in the air, buoyantly supported by the vapor |
| Lahars | Mix of water, mud, ash, and pyroclastic material |
| Hot Spots | Regions where mantle plumes breach the crust (ocean or continental) and form deposits; Mafic rocks |
| Phreatic Eruptions | Incredibly explosive eruptions that occur when rising magma reaches groundwater and vaporizes the water into steam quickly |
| Pluton | Collective term for intrusive igneous bodies that may be tabular, cylindrical, or massive including: Dikes, sills, laccoliths, volcanic pipes, batholiths, and stocks |
| Concordant Plutons | Boundaries parallel the layering of the host country rock |
| Discordant Plutons | Boundaries cut across the host country rock |
| Dike | Discordant tabular igneous body that cuts across the structure of adjacent rocks or massive rocks |
| Sill | Tabular igneous body that parallels the structure of surrounding rocks |
| Laccolith | A concordant igneous body that has a domed upper surface, a flat lower surface parallel to the surrounding rock and is fed by a dike at its thickest point |
| Volcanic Pipes | The central portion of a volcano through which magma is transported |
| Volcanic Neck | Vertical pipe-like intrusion that represents a former volcanic vent/pipe |
| Batholith | Large, usually discordant plutonic mass that covers mroe than 100 square kilometers at the Earth surface, with no known base |
| Stock | A plutonic mass that covers less than 100 square kilometers at the Earth surface, that is usually discordant but not always |
Created by:
FaithRaquel2015
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