Geology Lab Midterm

lineations (metamorphic)

in structural geology, these are linear structural features within rocks.

xenolith (igneous)

(Greek: foreign rock) is a rock fragment which becomes enveloped in a larger rock during the latter's development and hardening

what is a metamorphic rock?

- a rock that has been altered in form due to heat, pressure, and/or hydrothermically. -Changes in form include change in: crystal shape/habit (recrystallization), rock/mineral shape, mineralogy (different minerals can form in the rock due to metamorphism)

fossils as time indicators

-Law of Fossil Succession: organisms succeed each other in a definite and determinable order; no species evolves again once it has gone extinct -Law of Fossil Assemblages: groups of fossils commonly found together in specific time intervals. Ideally, the time interval will be the same regardless of the location

divergent boundary characteristics

-MOR (mid oceanic ridge) -sea floor spreading -up welling of molten material

biogenic rocks (sedimentary)

-Rocks that form as a result of biologic processes- i.e. rocks made of organic remains. These can be altered, or diagenetically altered -most are calcium carbonates (limestone and dolostone) -silicates (chert) -phosphatic rocks -plant remains (coal) -marine organics (oil shale and petroleum)

luster of minerals (metallic vs nonmetallic)

-a reflective property of mineral surfaces -metallic and submetallic -nonmetallic: decreasing reflectivity: adamantine, glassy/vitreous, resinous -other: pearly, greasy/oily, silky, dull, earthy

numerical dating

-absolute age in years

ultramafic rock (igneous)

-almost entirely magnesium and iron silicates -minerals: olivine, pyroxene -mafic mineral conent (86-100%) -rarely observed on the Earth's surface. believed to be major constituent of Earth's mantle. Commonly found as xenoliths in basaltic lavas -rock types: peridodite/pyroxenite, komatiite/picrite

correlation

-association of matching rocks of similar age from different locations -uses index fossils and fossil assemblages

intrusive vs extrusive igneous rocks

-based on when magma cools -intrusive: cool at depth (magma). This means that they cool at slower rates and therefore have larger crystals -extrusive: cool at the surface(lava). This means that they cool at faster rates and have smaller crystals

breakage of minerals

-cleavage: tendency of a mineral to break along flat planes of weaker bonding -fracture: cleavage is absent and mineral breaks irregularly

sedimentary contacts

-contact: surface between two different rock units -types of sedimentary contacts: conformable, noncomformable

mafic rocks (igneous)

-contains abundant ferromagnesian minerals (magnesium and iron silicates) -minerals: olivine, pyroxene, Ca-rich, plagioclase, (amphibole) -mafic mineral content: (46%-85%) -usually dark in color -characteristic of Earth's oceanic crust; Also found on the moon, Mars, and Venus. Forms a runny (low viscosity) lava rock types: gabbro, basalt

shape of mineral

-crystal habit: the shape that a crystal will take if it grows unimpeded -important: most mineral specimens are irregular grains, very few display their characteristic crystal habit

grain shape (sedimentary)

-distance the grains traveled before deposition -rounding: during transport, grains may be reduced in size due to abrasion(rounding off of sharp corners and edges of grains). Rounding of grains gives us clues to the amount of time a sediment has been in the transportation cycle -rounded: more travel time (lots of abrasion) -angular: less travel time (not as much abrasion)

grain size (sedimentary)

-distance the grains traveled before deposition -the smaller the grain size, the farther the grain traveled -gravel, sand, silt, clay

where would melting occur?

-divergent boundaries: decompression melting occurs -convergent boundaries:water is introduced to the system and the melting temperature drops

felsic rocks (igneous)

-dominated by silicon and aluminum (SiAl) -minerals: k-feldspar, plagioclase, quartz, biotite -mafic mineral content: 0-15% -light color, characteristic of continental crust. Forms a stiff (viscous) lava or magma -rock types:granite, rhyolite

beds & bedding planes (sedimentary)

-each bed=interval of deposition of that sediment -each bedding plane=break in depositional cycle -beds usually accumulate horizontally (Law of Original Horizontality)

evidence of plate tectonics

-earthquakes: generated at the plate margins -paleo-climate belts -exact deposits of continental glaciers are found in near equatorial Africa, South America, and India -the fossil record supports and gives credence to the theories of continental drift and plate tectonics -paleomagnetism: rocks that formed millions years ago contain a 'record" of the direction of the magnetic poles at the times of their formation -earth's magnetic field reversed periodically -recorded in minerals

fossils (sedimentary)

-environment of deposition -marine fossils (i.e shells): rock formed in marine environment, limestone -plant fragment fossils or terrestrial animal fossils (i.e tracks, bones): rock formed on land

igneous contacts

-extrusive: lava or pyroclastic flow deposit similar to sedimentary beds, cuase minor contact metamorphism to rocks below the flow -intrusive: younger that the bed it intrudes, the intruded rock is called the country rock. Can be a dike, sill, or pluton depending on size and orientation, dikes cut vertically, sills run horizontally

chemical properties (sedimentary)

-fizzes with HCl: made of calcite, probably a limestone of some sort -doesn't fizz with HCl: is not made of calcite

deformation associated with convergent boundary

-folding and faulting: uplift -reverse faults/thrust faults -compression

evaporites: a type of chemical sedimentary rock

-form by chemical precipitation in evaporating pools of water (grow in place) -usually look crystalline, but not always -examples: rock salt (halite), rock gypsum

chemical rocks (sedimentary)

-formed through the solution

gneissic banding (metamorphic)

-gneissic banding refers the alternating layers of light and dark minerals -mineral size is medium to coarse (visible to the eye) -represents high grade metamorphism

rock composition

-grains: clasts or crystals -grain size: coarse, medium, fine -grain shape: round to angular

grain sorting (sedimentary)

-how far grain traveled and energy level of transportation -degree of uniformity of grain size: -well sorted: grains are all the same size, low energy transportation, slow river, long travel time -poorly sorted: grains are different sizes, high energy transportation, debris slide, gravity flow, short travel time

slaty cleavage (metamorphic)

-if it has slaty cleavage, it is slate -slaty cleavage refers to the way the rock breaks into tabular sheets, roughly oblique to perpendicular in respect to the foliated crystals (usually mica) -no visible mica grains -slate usually does not have a sheen to it -represents low grade metamorphism

intermediate rocks (igneous)

-intermediate in composition between felsic and mafic -minerals: pyroxene, amphibole, plagioclase, biotite, quartz -mafic mineral content: 16-45% -rock types: diorite, andesite

conformable sedimentary contact

-layers deposited one after another with no gap or interruption in deposition -shows a full record of that time interval

sedimentary rock (pt2)

-made up of grains (rock fragments, minerals, and fossils) -two types of sedimentary rocks: clastic (detrital), chemical (includes biochemical-sometimes referred to as biogenic-and evaporites)

detrital/clastic sedimentary rocks

-made up of rock fragments and minerals -grains have usually been transported some distance -examples: conglomerate, breccia, sandstone, arkose, siltstone, shale/mudstone

metamorphic grade

-measure of how much the rock was metamorphosed -not related to the composition and mineralogy of protoliths -different metamorphic grades produce different mineralogy and textures

identifying metamorphic rocks

-metamorphic names reflect chemistry and texture (just like igneous rocks) -need to know texture type and mineral types present to know name of rock

crystalline texture (metamorphic)

-minerals are usually visible to the eye and look like crystals. -crystals are usually all the same size, and are medium to coarse grained -can be all sorts of colors -some will fizz with HCl

how do rocks form?

-molten rock cools and igneous rocks are formed -metamorphic rocks are formed when preexisting rocks are changes by temperatures and pressures -when loose grains/sediments undergo lithification, the result is a sedimentary rock

transform boundary characteristics

-mostly made up of transform faults (eg zones where rock bodies slip past each other)

phyllite texture (metamorphic)

-no visible mica grains -glossy/bright sheen -wavy to wrinkled foliation of mica grains -weak slaty cleavage -represents low to medium grade metamorphism

contact metamorphism

-occurs locally, next to igneous intrusions, or from hydrothermal fluids from intrusions -pressure is low to moderate -temperature is moderate to high

regional metamorphism

-occurs over large areas due to tectonic processes -pressure involved is moderate to high -temperature involved is low to high -associated with batholiths (only because these are associated with regional tectonics), rock burial (subduction), folding, Mt. building, etc caused by tectonics

chemical sedimentary rock

-ooids; distinctive sand-sized grains formed by precipitation of argonite around a central nucleus. Some ooids have concentric internal structure (fizzes with HCl) -examples: (oolitic or fossiliferous) limestone, dolostone, chalk, chert

relative dating

-placement in a sequence -older/younger -law of original horizontality: sediments and lava flows are deposited as horizontal layers (called bed or strata) -law of superposition: in underformed sedimentary rocks or lava flows, younger strata always lie on top of older strata -law of original (or lateral) continuity: at the time of deposition, beds extend in all directions until there are no more sediments or boundary is encountered -law of inclusion: rock fragment included in a bed has to come from an older feature than that bed -law of cross cutting relationships: when a fault or igneous intrusion cuts (crosses it in cross section) a feature, it is younger that that feature

absolute dating principles

-radioactivve decay is the emission if a particle from the nucleus of an unstable material (parent) -half-life is the amount of time it takes for half of the parent material to decay into the daughter material

foliation textures (metamorphic)

-refers to the layering and parallel alignment of mineral crystals. Foliation forms perpendicular to pressure -slaty cleavage, phyllitic texture, schistosity, gneissic banding

unconformable sedimentary structure

-represents a hiatus in deposition -results in a loss of time in the geologic record -can happen if erosion outpaces sediment deposition or if sediment supply is cutoff

glassy texture (metamorphic)

-represents low to medium grade metamorphism

cross bedding (sedimentary)

-result of sediment being transported (and deposited) in one direction by some current -can be big or small -relicts of dunes/current ripples -can indicate desert, river, or beach environments -can show paleocurrent direction

non foliated textures (metamorphic)

-rocks that have no obvious layering -4 main textures: crystalline, microcrystalline, sandy, glassy

sandy texture (metamorphic)

-sandy texture: feels and looks like sand -what could be the protolith? -very, very hard -composed

schistosity (metamorphic)

-schistocity refers to the foliation of visible platy minerals (mica) and/or linear alignment of prismatic minerals (tourmaline or hornblende) -minerals are visible -rock is covered in scaly/glittering layer of shiny minerals -can have wavy foliation -represents medium to high grade metamorphism

unconformities

-shows where erosion has taken place -angular: tilted layers overlain by younger flat beds -disconformity: older horizontal beds overlain by younger beds with a gap in time/loss of one or many units due to erosion -nonconformity: younger sedimentary beds over an older metamorphic or igneous layer

deformation associated with transform boundary

-strike slip fault or transform boundary -slide past one another/shearing -formation of mini basins and ranges

sedimentary structures

-structures form during or shortly after deposition of the sediment -some sedimentary structures are created by the water or wind which moves the sediment -other sedimentary structures form after deposition-such as footprint, worm trails, raindrop imprints or mucracks

convergent boundary characteristics

-subduction zones -volcanic arcs -island arcs -(ocean-ocean, ocean-continent, continent-continent)

fault contacts

-surface between two masses (often simplified to blocks) of rocks that slid or are sliding past one another -faults are always younger that the rock layers that they cut across -beds can be displaced (moved) along faults

igneous rock identification

-texture and minerals -remember compositional twins

cleavage of minerals

-the ability of a mineral to break or come apart in a consistent way -breakage is along atomic planes -cleavage is consistent with crystal symmetry and may be one to multi-directional from one mineral to another

distinctive properties of sedimentary rocks

-the grains of a sedimentary rock give us a story of the origin of the grains & what type of environment the rock formed in -5 types of properties that we look for (grain size, grain shape, sorting, fossils, chemical properties)

bowen's reaction series

-the theory of how different igneous rocks are formed -partial/fractional melting of upper mantle at divergent boundaries=mafic magmas -partial/fractional melting of subducted oceanic crust become intermediate and/or felsic magmas due to assimilation of host bedrock and/or fractional crystallization -viscosity: the state of being thick, sticky, and semifluid in consistency, due to internal friction

metamorphic textures

-there are two primary types of metamorphic textures: foliated and non-foliated

deformation associated with divergent boundary

-thinning of crust -subsidence -normal faulting -tension due to spreading -upwelling of molten material

metamorphic processes

-two main types of metamorphism -regional metamorphism -contact metamorphism

magma composition (igneous)

-ultramafic: rare, primitive, mantle derived -mafic: (Mg, Fe) rich, more dense, oceanic crust -intermediate: mix of mafic and felsic -felsic: (Al, Si) rich, less dense, continental crust

biogenic rocks

-usually made up of calcite in the form of shells or shell fragments -indicates marine environment -organisms produce calcite to form their shells -examples: fossiliferous, limestone, coquina, coal

color of minerals

-wavelengths of visible light are absorbed or reflected by the mineral -sometimes color is determined by trace elements -some minerals change color or have various forms of different color -cannot rely on color when it comes to mineral identification

The Earth's Layers (3 layers and sublayers)

Crust (continental and oceanic crust), Mantle (asthenosphere, upper mantle, lower mantle), core(outer core, inner core)

Fracture of minerals

Describes the inability of a mineral to break in a consistent way and and therefore not along cleavage planes

Earth's major lithospheric plates (7)

Pacific, North American, South American, African, Eurasian, Antarctic, Indo-Australian

hydrothermal veins (metamorphic)

a deposit of minerals found within a rock fracture that are not part of the host rock.

what is a rock?

a naturally occuring solid aggregate of one or more minerals or mineraloids

phenocryst (igneous)

a phenocryst is a relatively large and usually conspicuous crystal distinctly larger than the grains of the rock groundmass of a porphyritic igneous rock

What is a sedimentary rock?

a rock formed from the accumulation and consolidation of sediment, usually in layered deposits

conchoidal fracture of minerals

a smooth, curved breakage in all direction

minerals

a solid inorganic substance of natural occurrence. 5 things: inorganic, naturally occurring, solid, definite crystalline structure, definite chemical composition

sediment

an accumulation of chemical residues and fragmented rocks, mineral crystals, plants, or animals

macrofossil groups

brachipods (invertebrate shells), trilobites (arthropods), mollusks(invertebrates with asymmetrical shells), plants, reptiles, mammals, amphibians, fish

how are sedimentary rocks formed

clastic 1. weathering: the process of breaking down rocks and minerals into smaller pieces by water, wind, ice. This created grains 2. erosion (transport) & deposition: grains are transported by wind or water, variable distances. Deposition occurs in various location and is directly related to the energy of the environment 3. lithification: the hardening of sediment through compaction and cementation. This forms the rock 3. lithification

streak of minerals

color of powdered mineral which is tested by rubbing the mineral across a porcelain streak plate

igneous structures

common structures of intrusive igneous rocks: batholith (large intrusion of magma), sill (horizontal intrusion of magma), dike (vertical intrusion of magma), volcanic neck (core of volcano) common structure of extrusive igneous rocks: lava flows, volcanic cones (made of lava or pyroclastics), pyroclastic flows (kmade of pyroclastics- ash, lapili, and volc. bombs)

driving force of plate tectonics

convection cells: drag and move the lithospheric plates hotspots: injection of magma

Plate boundary types

convergent, divergent, transform

igneous texture aphanitic

crystals are too small (<1mm) to see, shows very fast cooling, (volcanic i.e from lava)

rhyolite (igneous)

derives from the rapid cooling of a very viscous magma of granitic composition; as a result it is mainly found in domes, chimneys, dikes, and more rarely in proper lava flows generally pyroclastic or aphanitic

rock texture

description of the grains and other parts of a rock: size, shape, arrangement -glassy-fine to coarse grained -vesicular, crystalline, foliated, clastic

effervesces with HCl

fizz or give off bubbles

igneous rock

formed when magma or lava cools

index fossils

fossil characteristics of a certain time that allow for easy age determination of rock units and correlation

weathered

fragmented into grains, chemically decayed to residues, or even dissolved

igneous textures: pyroclastic

fragments of volcanic glass, ash, cinders, volcanic bombs

flow banded rhyolite (igneous)

friction and viscosity of the magma causes phencrysts and xenoliths within the magma or lava to slow down near the interface and become trapped in a viscous layer. This forms laminar flow, which manifests as a banded, streaky appearance

igneous texture: glassy

glassy- looks like glass. Very rapid cooling (quenching), forms volcanic glass, no crystals present

mineral groups

grouped by chemical composition -Native Elements -SIlicates -oxides -hydroxides -sulfides -sulfates -carbonates -halides -phosphates

Lithification

hardened (compaction and cementation)

hardness of minerals

harder objects scratch softer objects

evidence for direction and rate of plate movement

hot spots: -an area of unusual volvanic activity -not associated with plate boundaries -youngest at the hotspot -cool-->dense--> subside--> erosion-->seamounts -volcanic islands created by hotspots allow us to track the rate and direction of plate movement

mudcracks and raindrop impressions (sedimentary)

indicates deposition above sea level on dry land, exposed to atmosphere -mudcracks=dry environment -raindrops= that it rains (can really assume if area is prone to heavy precipitation or not)

type of igneous rocks and where they form

mafic: oceanic crust is created where at divergent boundaries. Hot spots also tend to be mafic felsic: a magma chamber that pushes itself through a continental plate tends to be felsic intermediate: volcanic arcs

textures of igneous rocks

pegmatic, phaneritic, porphyritic, aphanitic, vesicular, glassy, pyroclastic

porphyroblastic texture (metamorphic)

refers to the uneven granular texture of a rock caused by the presence of large crystals, or porphyroblasts, in a fine grained groundmass

igneous texture: vesicular

rock contains vesicles (gas bubbles trapped in lava, which form from depressurization of the magma. often looks like a sponge (usually volcanic)

physical properties of minerals

shape, color, luster, hardness, streak, cleavage, texture, magnetism, specific gravity, taste, odor, effervesces with HCl

Magnetism of minerals

some minerals are magnetic. this ranges from weakly to strong magnetic

taste of minerals

some minerals exhibit a specific taste (halite and sylvite)

welded tuff (igneous)

the ash, pumice, and clasts were so hot that they remelted to form a glassy rock after landing on the ground. Most of the thin clasts are pumice blocks that collapsed and flattened as they were reheated

plate tectonics

the earth's lithosphere is broken into several large rigid slabs called plates, plates are moving apart along the mid-ocean ridges

Continental drift

the idea that the present day continents were once part of a single supercontinent

specific gravity of minerals

the specific gravity of a material is a comparison of its weight with the weight of an equal volume of water. Specific gravity measures the density of a material

igneous texture: porphyritic

two distinct crystal sizes, large ones and small ones. Generally due to a change in the rate of cooling

tuff (igneous)

type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption

igneous texture: pegmatic

very large crystals (many >2cm), shows very slow cooling (plutonic)

igneous texture: phaneritic

visible crystals, shows slow cooling, usually 1-10mm (plutonic)

erosion

worn away