igneous rocks. rock vs. mineral rock- a naturally formed consolidated material composed of grains of...
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Rock vs. Mineral
• Rock- a naturally formed consolidated material composed of grains of one or more minerals.
• Mineral- a naturally occurring element or compound with a relatively constant chemical and structural composition.
Three Rock Types1. Igneous: Rock formed from the cooling of
magma
2. Sedimentary: Rock formed from the accumulation and lithification (cementing) of weathered material.
3. Metamorphic: Rocks formed by the altering existing rock by heat and/or pressure.
Identification of Igneous Rocks
Texture: the size of the grains that make up the rock
Mineralogy: the minerals present in the rock
Textures:
Phaneritic (Fan-er-itic): all large grains Aphanitic (A-fan-itic): all small grains
Porphyritic (Poor-for-itic): large crystals surrounded by fine-grained matrix
Terms to explain to chemistry of igneous rocks:
• Mafic: (May-fik) Silica deficient igneous rocks with a high content of Magnesium, Iron, and Calcium. More dark minerals than light minerals.
• Felsic: (fell-sick) Silica rich igneous rock with a high percentage of potassium and sodium. Usually lots of quartz and feldspar.
Shiprock, New Mexico
Formed when a volcano goes extinct (loses its heat source). The magma that was inside the volcano cools and hardens into a rock much harder than that on the surface.
Eventually the volcano is weathered away, exposing the rock.
Magma Formation• molten rock created near the subduction zone.
• granitic magma ~ 650o C
• geothermal gradient – 3o C/100 m
• melting point increases with pressure; pressure increases with depth.
• mineral melting point is lowered by water under pressure.
Volcanism and Extrusive Rocks
• pyroclastic (pyro = “fire”; clast = “broken”)• pyroclastic flow- mixture of gas and pyroclastic
debris.
• caldera-• pumice-• vesicles-• cinder cone-
Extrusive Rockspyroclastic flow(click the picture below for a short video pumice with vesicles