Fluent Essays

Geology CHECK ATTACH Find an event that occurred this week that moves you. You must be able to relate it to the current chapter in some way – creativity is welcome. For instance, let’s say you read about the war in Afghanistan and parts of Pakistan. After reading the article, you check a world map and find that some remote parts of Pakistan are near the Himalayan Mountain Range. You will discover in Chapter 3 that the Himalayas were formed by a convergence of two continental plates, the Indian plate and the Eurasian plate, which causes a convergence zone that resulted in mountain uplift. And, voila!, the Himalayans are formed. Remember, geology is all about connections. The physical environment always sets the context for human events, and, often, they have a more direct influence than you may initially imagine. For example, you’re not worried about a tsunami if you live in North Dakota, but you are much more aware of the Pleistocene glaciations than you would be if you lived in Arizona. You may use an article from the following sources: Reuters National Public Radio Another news outlet if you include a paragraph telling me why you chose it. Turn in: A document that includes the entire story (copy and pasted from the original site). The citation (where you got it and when). The link. A map of the location of the event that was not included in the article. Paragraph of what you think about the news (good, bad, indifferent – just tell me why). Paragraph explaining at least one geologic connection that relates to this week’s chapter. Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks • Aggregated solids of minerals. • Three major types of rocks classified by origin, the way the rocks formed. • Fundamental links between rocks and environment (resources, sources for acid rain drainage, land subsidence, structure foundation failures, etc.). • Rocks deform in response to geologic forces/stress. Rocks Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Igneous Rocks  Solidified molten rock.  1,100°C to 650°C.  Temp depends on composition.  Earth is mostly igneous rock.  Magma – Subsurface melt.  Lava – Melt at the surface.  Volcanoes erupt magma. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Igneous Rocks  Melted rock can cool above or below ground.  Intrusive igneous rocks – Cool slowly underground.  Extrusive igneous rocks – Cool quickly at the surface. Lava – Cooled liquid. Pyroclastic debris – Cooled fragments. Volcanic ash. Fragmented lava.  Many types of igneous rocks.  All oceanic crust.  Most continental crust. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks What is Magma Made of?  Magmas have three components (solid, liquid and gas).  Solid – Solidified mineral crystals are borne by the melt.  Liquid – The melt itself is comprised of mobile ions. Dominantly Si and O; lesser Al, Fe, Mg, and K. Other ions present to a lesser extent.  Different mixes of elements yield different magmas. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks What is Magma Made of?  Gas – Magmas contain abundant dissolved volatile gas. Dry magma – Scarce volatiles. Wet magma – To 15% volatiles. Water vapor (H2O) Carbon dioxide (CO2) Sulfur dioxide (SO2) Nitrogen (N2) Hydrogen (H2) Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Magma Compositions  There are four major magma types based on silica (SiO2) percentage.  Felsic (feldspar and silica) 66 to 76% SiO2.  Intermediate 52 to 66% SiO2.  Mafic (Mg and Fe-rich) 45 to 52% SiO2.  Ultramafic 38 to 45% SiO2. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Magma Compositions  Composition controls magma density, T, and viscosity.  The most important factor is silica (SiO2) content. Silica-rich magmas are thick and viscous. Silica-poor magmas are thin and “runny.”  These characteristics govern eruptive style. Type Density Temperature Viscosity Felsic Very low Very low (600 to 850°C) Very High: Explosive eruptions. Intermediate Low Low High: Explosive eruptions. Mafic High High Low: thin, hot runny eruptions. Ultramafic Very high Very high (up to 1300°C) Very low. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Igneous Environments  Two major categories – Based on cooling site.  Extrusive settings – Cool at or near the surface. Cool rapidly. Chill too fast to grow big crystals.  Intrusive settings – Cool at depth. Lose heat slowly. Crystals grow large.  Most mafic magmas extrude.  Most felsic magmas don’t. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Interlocking or crystalline texture Igneous Textures  The size, shape, and arrangement of the minerals.  Interlocking – Mineral crystals fit like jigsaw puzzle pieces.  Fragmental – Pieces of preexisting rocks, often shattered.  Glassy – Made of solid glass or glass shards. Glassy texture Fragmental texture Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Crystalline Igneous Textures  Texture reveals cooling history.  Aphanitic (finely crystalline). Rapid cooling. Crystals do not have time to grow. Extrusive.  Phaneritic – (coarsely crystalline). Slow cooling. Crystals have a long time to grow. Intrusive. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Igneous Classification  Classification is based upon composition and texture.  Composition – Felsic, intermediate, mafic, and ultramafic.  Texture – Fine (aphanitic); coarse (phaneritic). Type Aphanitic (fine) Phaneritic (coarse) Felsic Rhyolite Granite Intermediate Andesite Diorite Mafic Basalt Gabbro Ultramafic Very high Very high (up to 1300°C) A B A B C2 C1 C2C1 Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks  Form by very rapid cooling of lava in water or air.  Glassy textures are more common in felsic magmas.  They often preserve gas bubbles (vesicles).  Underwater, basalt lava quenches into “pillows.” Glassy Textures Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Glassy Classification  Glassy Igneous Rocks.  Obsidian – Volcanic glass from rapidly cooled lava. Quenching – Lava flowing into water. High silica lavas – These can make glass without quenching.  Pumice – Frothy felsic rock full of vesicles; it floats.  Scoria – Glassy, vesicular, mafic rock. Pumice Scoria Obsidian Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Fragmental Textures  Preexisting rocks that were shattered by eruption.  After fragmentation, the pieces fall and are cemented. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Fragmental Classification  aka Pyroclastic – Fragments of violent eruptions.  Tuff – Volcanic ash that has fallen on land and solidified.  Volcanic breccia – Made of larger volcanic fragments. Tuff Breccia Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Sedimentary Rocks  Sediments are the building blocks of sedimentary rocks.  Sediments are diverse, as are the rocks made from them.  Four classes:  Clastic – Made from weathered rock fragments (clasts).  Biochemical – Cemented shells of organisms.  Organic – The carbon-rich remains of plants.  Chemical – Minerals that crystallize directly from water. ChemicalClastic OrganicBiochemical Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Clastic Sedimentary Rocks  Clastic sedimentary rocks reflect several processes.  Weathering – Generation of detritus via rock disintegration.  Erosion – Removal of sediment grains from rock.  Transportation – Dispersal by wind, water, and ice.  Deposition – Settling out of the transporting fluid.  Lithification – Transformation into solid rock. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks  Lithification – Transforms loose sediment into solid rock.  Burial – More sediment is added onto previous layers.  Compaction – Overburden weight reduces pore space. Sand – 10 to 20% Clay – 50 to 80%  Cementation – Minerals grow in pores, “gluing” sediments. Clastic Sedimentary Rocks Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Clastic Sedimentary Rocks  Clast (grain) size – The average diameter of clasts.  Range from very coarse to very fine.  Boulder, cobble, pebble, sand, silt, and clay.  With increasing transport, average grain size decreases. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Clastic Sedimentary Rocks  Angularity and sphericity – Indicate degree of transport.  Fresh detritus is usually angular and non-spherical.  Grain roundness and sphericity increases with transport.  Well-rounded – Long transport distances.  Angular – Negligible transport. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Clastic Sedimentary Rocks  Sorting – The uniformity of grain size.  Well-sorted – Uniform grain sizes.  Poorly sorted – Wide variety of grain sizes.  Sorting becomes better with distance from source. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Clastic Sedimentary Rocks  Coarse clastics – Composed of gravel-sized clasts.  Breccia – Comprised of angular fragments. Angularity indicates a lack of transport processing. Deposited relatively close to source. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Clastic Sedimentary Rocks  Coarse clastics – Composed of gravel-sized clasts.  Conglomerate – Comprised of rounded gravel. Indicates water transport. Clasts bang together forcefully in flowing water. Collisons round angular corners and edges of clasts. Conglomerates are deposited at a distance from the source. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Clastic Sedimentary Rocks  Sandstone – Clastic rock made of sand-sized particles.  Forms in many depositional settings.  Quartz is, by far, the dominant mineral in sandstones.  Sandstone varieties.  Arkose – Contains abundant feldspar.  Quartz sandstone – Almost pure quartz. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Clastic Sedimentary Rocks  Fine clastics - Composed of silt and clay.  Silt-sized sediments are lithified to form siltstone.  Clay-sized particles form shale.  Fine clastics are deposited in quieter waters.  Floodplains, lagoons, mudflats, deltas, deep-water basins.  Organic-rich shales are the source of petroleum. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks  These are sediments derived from living organisms.  Biochemical – Hard mineral skeletons.  Organic – Cells of plants, algae, bacteria and plankton. Biochemical and Organic Rocks Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Biochemical Rocks  Biochemical limestone – CaCO3 skeletal (shell) remains.  Warm, tropical, shallow, clear, O2-rich, marine water.  Diverse organisms (plankton, corals, clams, snails, etc.).  Many textural varieties. Reefs. Shell debris. Lime mud (micrite). Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks  Made from organic carbon.  Coal – Altered remains of fossil vegetation. Accumulates in lush tropical wetland settings. Requires deposition in the absence of oxygen.  Oil shale – Shale with heat altered organic matter. Organic Rocks Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Chemical Sedimentary Rocks  Comprised of minerals precipitated from water solution.  Evaporites – Created from evaporated seawater.  Evaporation triggers deposition of chemical precipitates.  Examples include halite (rock salt) and gypsum. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Chemical Sedimentary Rocks  Dolostone – Limestone altered by Mg-rich fluids.  CaCO3 altered to dolomite CaMg(CO3)2 by Mg 2+-rich water.  Dolostone looks like limestone, except… It has a sugary texture and a pervasive porosity. It weathers to a buff, tan color. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rocks  Metamorphic – Changed from an original “parent.”  Meta = Change.  Morph = Form or shape.  Parent rocks are called “protoliths.”  Metamorphism can occur to any protolith. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rocks  Protoliths undergo pronounced changes in…  Texture.  Mineralogy.  Due to changes in…  Temperature.  Pressure.  Tectonic stress.  Reaction with heated water. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Character  Metamorphic rocks have distinctive properties.  Unique texture – Intergrown and interlocking grains.  Unique minerals – Some that are only metamorphic.  Unique foliation – A planar fabric from aligned minerals.  These transformations can change the rock completely. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Processes  Metamorphic change occurs slowly in the solid state.  Several processes are at work.  Recrystallization – Minerals change size and shape.  Phase change – New minerals form with… Same chemical formula. Different crystal structure. Example: Kyanite. KyaniteKyanite Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Processes  Neocrystallization – New minerals with changes in temperature and pressure.  Initial minerals become unstable and change to new minerals. Original protolith minerals are digested in reactions. Elements restructure to form new minerals.  In this way, a shale can transform into a garnet mica schist. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Causes of Metamorphism  The agents of metamorphism are…  Heat (T).  Pressure (P).  Compression and/or shear.  Hot water.  Not all agents are required; they often do co-occur.  Rocks may be overprinted by multiple events. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Heat (Temperature, T)  Metamorphism occurs as the result of heat.  Temperature (T) ranges between 200oC and 850oC.  The upper T limit is…melting. It varies based upon rock mineral composition and water content.  Heat energy breaks and reforms atomic bonds.  Sources of heat.  Magmatic intrusions.  Compression. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Pressure (P)  P increases with depth in the crust.  270 to 300 bars per km (1 bar is almost 1 atm = 14.7 psi).  Metamorphism occurs mostly in 2 to 12 kbar range.  T and P both change with depth.  Mineral stability is highly dependent upon T and P.  This stability can be graphed on a “phase diagram.”  Changes in T and P lead to changes in minerals. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks  Pressure that is greater in one orientation.  A commonplace result of tectonic forces.  Two kinds of differential stress: Normal and shear.  Normal Stress – Operates perpendicular to a surface. Tension – Pull-apart normal stress. Compression – Push-together normal stress. Differential Stress Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Differential Stress  Two kinds of differential stress: Normal and shear.  Shear Stress – Operates sideways across a surface. Causes material to be “smeared out.” Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks  At higher T and P, differential stress deforms rock.  Rocks change shape slowly without breaking. Differential Stress Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rock Types  Two major subdivisions of metamorphic rocks.  Foliated – Has a through-going planar fabric. Subjected to differential stress. Classified by composition, grain size, and foliation type. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rock Types  Two major subdivisions of metamorphic rocks.  Nonfoliated – No planar fabric evident. Crystallized without differential stress. Classified by mineral composition. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rocks  Slate – Fine clay, low-grade metamorphic shale.  Has a distinct foliation called slaty cleavage. Develops by parallel alignment of platy clay minerals. Slaty cleavage oriented perpendicular to compression. Slate breaks along this foliation creating flat sheets. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rocks  Phyllite - Fine mica-rich rock.  Formed by low- to medium-grade alteration of slate.  Clay minerals neocrystallize into tiny micas.  Micas reflect a satiny luster.  Phyllite is between slate and schist. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks  Schist – Fine or coarse rock with larger micas.  Medium- to high-grade metamorphism.  Has a distinct foliation called schistosity. Parallel alignment of large mica crystals. Micas are visible because they have grown at higher T.  Schist often has other minerals due to neocrystallization. Quartz. Feldspars. Kyanite. Garnet. Staurolite. Sillimanite.  Large non-mica minerals are called porphyroblasts. Metamorphic Rocks Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rocks  Gneiss – Has a distinct banded foliation.  Light bands of felsic minerals (quartz and feldspars).  Dark bands of mafic minerals (biotite or amphibole). Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Migmatite  Migmatite is a partially melted gneiss.  It has features of igneous and metamorphic rocks.  Mineralogy controls behavior.  Light-colored (felsic) minerals melt at lower T.  Dark-colored (mafic) minerals melt a higher T.  Felsics melt first; mafics remain metamorphic. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rocks  Nonfoliated rocks lack a planar fabric.  Absence of foliation possible for several reasons: Rock not subjected to differential stress. Dominance of equant minerals. Absence of platy minerals like clays or micas. Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rocks  Amphibolite – Dominated by amphibole minerals.  Basalt or gabbro protolith.  Usually not well foliated.  Hornfels – Alteration by heating.  Associated with plutonic intrusions.  Finely crystalline. Amphibolite Hornfels Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rocks  Quartzite – Almost pure quartz in composition.  Forms by alteration of quartz sandstone.  Sand grains in the protolith recrystallize and fuse.  Like quartz, it is hard, glassy, and resistant. Metamorphic Alteration Edited by Joao Santos Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks Metamorphic Rocks  Marble - Coarsely crystalline calcite or dolomite.  Forms from a limestone or dolostone protolith.  Extensive recrystallization completely changes the rock.  Original textures and fossils in the parent are obliterated.  Used as a decorative and monument stone.  Exhibits a variety of colors. Metamorphic Alteration Edited by Joao Santos