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Geology 201 Lab Midterm

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159 Terms
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planar bedding
asymmetrical ripples
symmetrical ripples
cross bedding
graded bedding
drumlin
esker
braided stream
meandering stream
oxbow lakes
shell with 2 valves that are not identical, but each valve is bilaterally symmetrical on itself. often ribbed valve surfaces with wing-like extensions on either side
altered: permineralization *hint this is a bone
internal mold shell commonly with 2 identical valves (mirror images) joined by a hinge. has a raised protuberance called an umbo arises near the hinge
external mold segmented organism divided into 3 parts; head (cephalon), body (thorax), and tail (pygidium) this particular fossil only shows the head of this organism
this sticky substance that hardens to a crystal-like form is capable of producing unaltered remains through embedding
altered: recrystallization this is an organism that was recrystallized in dolostone
unaltered remains shell commonly with 2 identical valves (mirror images) joined by a hinge. has a raised protuberance called an umbo arises near the hinge *hint, not a brachiopod
altered: petrification *hint, not an animal
altered: dessication *hint, not an animal
altered: carbonization
occurs due to animals creating feeding/dwelling tunnels
occurs due to animals creating feeding/dwelling tunnels
occurs due to animals creating feeding/dwelling tunnels
occur due to animals feeding or dwelling
polygonal or rounded cylindrical corallites arranged in geometric patterns or chains that may be tightly cemented or loosely packed
segmented organism divided into 3 parts; head (cephalon), body (thorax), and tail (pygidium)
extinct sea creature with a flat, spiral shell
spiral shaped, often conical, unsegmented shells. opening is called an aperture (where organism comes out) and tip is the apex
stalked cylindrical animal (not a plant) with root-like base and bulbous, branched top. commonly breaks apart with only ossicles preserved (stacked cheerio or star shaped discs making up the stem)
*cleavage - 1 direction vitreous lustre common in metamorphic and felsic igneous rocks H = <2.5 (scratched by fingernail) *distinguished from muscovite only by colour
*cleavage - 3 not at 90 *reacts strongly with HCl vitreous common in sedimentary rocks and marble H = 3
*cleavage - 3 not at 90 *reacts weakly with HCl when powdered common in sedimentary rocks H = 3
3 at 90 to each other *bright metallic lustre *high density (contains lead) H = <2.5 (scratched by penny)
no cleavage *dodecahedral habit (soccer ball shape) common in metamorphic rocks *H = >6 (scratches porcelain)
cleavage - 3 at 90 translucent to transparent *tastes like salt common in evaporate sedimentary rocks H = <3 (scratched by steel nail)
no cleavage *metallic lustre - sparkly + bright unoxidized - dull metallic when oxidized *red-brown streak *colour can be dark grey or red-brown depending on oxidation level weakly magnetic
*cleavage - 2 not at 90° common in intermediate igneous rocks and amphibolite (metamorphic) rocks *columnar habit H = 5-6 *distinguished from pyroxene by habit
cleavage - 2 at 90° *perthitic texture (exsolution) common in high-grade metamorphic rocks, clastic sedimentary rocks, and felsic igneous rocks H = 6 (scratches glass but not porcelain)
cleavage - 2 not at 90° typically blue in colour *bladed habit *differential hardness (H = 5 and 7)
*cleavage - 1 direction *distinguished from biotite only by colour (colourless) vitreous lustre transparent common in metamorphic and felsic igneous rocks H = <2.5
no cleavage *granular habit (sugar crystals) common in mafic igneous rocks *typically apple-green in colour H = >6.5 (scratches porcelain)
cleavage - 2 at 90° *twin striations common in igneous rocks and high grade metamorphic rocks H = 6 (scratches glass, but not porcelain)
bright metallic lustre *dark grey-green streak *brassy yellow (can brown if weathered) blocky or massive habit
cleavage - 2 at 90° common in mafic igneous rocks *blocky habit H = 5-6 (can scratch glass plate) only distinguished from hornblende by habit
no cleavage *concoidal fracture (circular) common in felsic igneous rocks, high-grade metamorphic rocks, and clastic sedimentary rocks massive and/or prismatic habit *H = 7 (scratches porcelain)
texture: aphanitic and porphyritic intermediate composition - dominantly hornblende, alkali feldspar, plagioclase feldspar when only aphanitic hard to identify except by colour - often has a green-grey or grey-beige hue extrusive rock -porphyritic rocks considered extrusive phenocrysts are often feldspars -alkali feldspar can weather to a chalky appearance
equigranular and aphanitic mafic composition -dominantly pyroxene, olivine, and plagioclase feldspar very dark grey or black colour can sometimes be mistaken for a mudstone, but these are much harder -cannot be scratched easily with steel nail can sometimes be mistaken for fine-grained amphibolites, but these appear duller -dominated by pyroxene which is duller than hornblende, which dominates amphibolites
texture: phaneritic and porphyritic intermediate composition -dominantly alkali feldspar, biotite, hornblende, and plagioclase feldspar commonly has a S&P look to it with a 50/50 split of light and dark minerals can be confused with granite -dark grains->granites will be mostly biotite, diorite has more hornblende (not scratched by steel nail) phenocrysts in this sample are plagioclase feldspar
texture: equigranular and phaneritic mafic composition -dominantly pyroxene, olivine, and plagioclase feldspar often mistaken for amphibolite -cleavage only way to tell (pyroxene=gabbro, hornblende=amphibolite) some gabbros can look similar to diorites when they have a lot of plagioclase in them (light grey), but still dominantly dark in colour
texture: equigranular and phaneritic felsic composition -dominantly alkali feldspar, quartz, and biotite this kind aka pink granite -occurs when alkali feldspar is pink in colour quartz can be difficult to pick out from feldspars in this rock
texture: aphanitic and porphyritic felsic composition -dominantly quartz, alkali feldspar, and biotite - can also include small amounts of plagioclase feldspar and hornblende at times often light grey, cream, or light pink in colour in this sample, the phenocrysts are hornblende -columnar habit + cannot be scratched by steel nail
texture: glassy and vesicular always has a glassy texture -no ordered mineral structure this sample also shows a vesicular texture -lava that cooled was water rich so gas bubbles formed can be black or brown in colour will show concoidal fracture when broken
texture: aphanitic and vesicular mafic composition -dominantly pyroxene, olivine, and some plagioclase feldspar very dark grey or black in colour -can sometimes see lighter grey crystals in it which are plagioclase feldspars vesicular texture -lava was water rich and contained gas bubbles easier to identify than non-vesicular basalt
texture: medium grained, moderately sorted pinkish colour of clasts are often an indication of feldspar grains (make up more than 50% of rock) grain size mostly the same = moderately sorted
texture: coarse grained, well sorted >95% quartz grains (will scratch porcelain) range of grain sizes from coarse to very coarse rock shows graded bedding structure as well
texture: medium grained, well sorted >50% lithic grains rock shows range of grain sizes in the medium range yellow colour in this sample is the result of iron oxidation
texture: pebble sized grains, poorly sorted very angular clasts very mixed composition very immature rock very poorly sorted
texture: pebble sized grains, poorly sorted rounded clasts mixed composition immature rock poorly sorted
texture: clay sized grains, fissile very soft rock easily mistaken for mudstone but shows fissility easily mistaken for siltstone but clay grains are less 'gritty' than silt grains
texture: silt sized grains, very well sorted very soft rock can see some distinct grains in rock easily mistaken for mudstone, but silt grains are "grittier" clay grains
mud dominated fossils in this case are amphipora (type of sponge) this sample is dolomitic (**changes name)
high energy environment of formation corals = fossils corals are in "life position" so the rock is a boundstone, even though there is often very little mud like in packstones and grainstones
grain dominated packstone vs grainstone -if mud were removed from the specimen, the grains would not hold together in a packstone, but would in a grainstone crinoids = fossils crinoids ≠ ooids -crinoids have hollow centers, ooids are solid
grain dominated packstone vs grainstone -if mud were removed from the specimen, the grains would not hold together in a packstone, but would in a grainstone crinoids = fossils crinoids ≠ ooids -crinoids have hollow centers, ooids are solid
0-5% fossils or ooid grains mud is carbonate very low energy environment formation often massive, no evidence of bedding or other structures
grain dominated packstone vs grainstone -if mud were removed from the specimen, the grains would not hold together in a packstone, but would in a grainstone ooids are spherical ooids ≠ fossils ooids vs pisoids - ooids <2mm in diameter, pisoids >2mm in diameter
low energy environment identified by multiple, very thin layers that form domes stromatolites = alternating layers of mud and cyanobacteria (blue/green algea) stromatolites are in "life position"
texture: non-foliated protolith = gabbro or basalt dominated by amphibolite (hornblende) and plagioclase feldspar can sometimes contain garnet or porphyroblasts - will either be randomly scattered, or limited to small lenses of plagioclase in the rock if present often mistaken for gabbro or basalt - dominantly hornblende, will appear more vitreous
texture: foliated low grade rock protolith = mudstone or shale usually have a grey-green colour typically feel slippery and have a pearly lustre
texture: porphyroblastic, crenulated, and foliated low grade rock this sample contains very small magnetite porphyroblasts in it can show crenulated texture - series of micro folds throughout rock, bumpy surface note: porphyroblasts ≠ phenocrysts and porphyritic texture ≠ porphyroblastic texture (igneous vs metamorphic)
texture: foliated protolith = shale or mudstone can be mistaken for gneiss medium to high grade rock
texture: porphyroblastic and foliated medium to high-grade rock - this sample is high grade due to kyanite in rock porphyroblasts = garnet + kyanite note: porphyroblasts ≠ phenocrysts and porphyritic texture ≠ porphyroblastic texture (igneous vs metamorphic)
texture: foliated protolith = shale/mudstone or felsic igneous rock very high grade rock (often seen in garnet zone) can be mistaken for schist strong foliation in alternating bands of light and dark mineral (do not confuse with marble)
texture: non- or weakly foliated protolith = limestone (can be dolostone if reacts weakly with HCl) can sometimes see remnant fossils in the rock if at a low enough grade sometimes mistaken for quartzite (which does not react with acid and is much harder, cannot be scratched by steel nail)
texture: non-foliated protolith = conglomerate can be any colour can be mistaken for conglomerate
texture: foliated very low grade rock protolith = shale or mudstone often mistaken for shale - has a slight sheen, shale is dull usually medium to dark grey colour can contain remnant fissility if the protolith was a shale
texture: non-foliated protolith = sandstone (more specifically, quartz arenite) - composition is almost completely quartz which also makes the rock very hard can be any colour often mistaken for sandstone or marble (no pore space and is much harder)