lab test one Flashcards
phaneritic texture
coarse grained
mineral grains are large enough to see with unaided eye
intrusive texture
magma cooled slowly to allow for crystals to grow
vesicular/ frothy
lava contained large amounts of gas (like CO2)
extrusive
lava cooled so quickly that no minerals could form
will most likely have felsic composition
physical/mechanical weathering
processes that break rock without changing its chemical composition or properties
ex. frost wedging + heat expansion
medium grained
SIZE
detrital
sand-sized
grains between 1/16 mm and 2 mm
grains can be angular or rounded
oolitic texture
chemical
composed of rounded oolites
oolites are made of calcite
two types of foliation
layered or banded
metallic characteristics
shiny?
ign. intrusive textures definition
rocks that form from magma that cools below the surface
felsic
Minerals: Potassium Feldspar, Quartz, Biotite, Muscovite
Color: Pinkish, Red, White, Light Gray (Also, rocks with a glassy texture of all colors)
SiO2 Content: High
mafic
means iron + magnesium
Minerals: Ca-Plagioclase, Pyroxene (Augite), Olivine
Color: Black, Faded Black, Red (vesicular only)
SiO2 Content: Low
tectonic environments
subduction zones + riffs/hot spots
riffs/hot spots
mafic rocks
what makes a rock sedimentary?
form from the accumulation of sediments
sediments are generally formed through some weathering process
- the only rocks with fossils in them
- provide geological records
- chairs, gas, etc.= fossil fuels
chemical weathering
chemical processes that cause chemical changes that break down rock
ex. dissolution + oxidation
detrital texture characteristics
compromised of mineral fragments held together by cement
textures are described based on their particle size
- coarse grained
- medium grained
- fine grained
- very fine grained
fine grained
SIZE
“fine grained/silt sized”
detrital
silt-sized grains; between 1/256 mm and 1/16 mm
will often feel smooth to skin but rough to fingernail
often the mineral quartz
crystalline texture
chemical
compromised of crystals large enough to distinguish with the eye
composed of minerals softer than glass
*calcite, gypsum, hallite
foliation
indicates that metamorphism has affected rocks
what makes it a mineral?
must be five things
- solid
- naturally occurring
- inorganic (usually)
- definite but not fixed, chemical composition
- ordered internal arrangement (crystalline structure)
what is color?
simply the color you see when you observe a sample
be able to explain what “streak” is and why it is important
color that a powdered sample has.
light can transmit through the small powder particles
luster
a minerals appearance when light is reflecting off its surface
two main categories
luster’s two main categories
metallic vs. non metallic
non-metallic characteristics
glass, pearly, dull, fibrous
striations
look like small parallel lines etched into a minerals face
caused by mineral twinning
you may not be able to see it in all samples of minerals that have striations
hardness
a materials resistance to being scratched
tenacidy
when the material is hit
cleavage
what a mineral does when it breaks upon a plane of weakness
1-direction cleavage
basal, sheety
@ 90 degrees= blocky
not @ 90= splinters, oblique cleavage
3-direction cleavage
@ 90 degrees= cubic
not @ 90= rhombic
4-direction cleavage
octahedral
6-direction cleavage
dodecahedral
know each of the physical property tests, how they work, how to do them, and what they tell about the mineral being tested
Moh’s scale of hardness (fingernail, glass test, acid test)
be able to recognize and identify “special” properties
10
smell taste acid reaction magnetism feel flexibility elasticity conchodrial feature (vs. uneven) striations high density
what is a rock?
a solid aggregate of minerals
with a few minor exceptions, a rock consists of pieces of mineral material held together in some fashion
what makes a rock igneous?
rocks that form from the cooling of a melt
consists of interlocking crystals of minerals that form while these melts cool
these crystals can be large enough to see or may require a microscope + a thin section of the rock
- no layering or foliation
- mainly composed of silicate minerals, therefore almost always dense and hard
geologists name melts based on _________
their relation to the surface
below: magma
at or above: lava
rock textures
texture= important
has nothing to do with how the rock “feels”
describes:
grain shape
grain size
grain orientation
ign. extrusive textures definition
rocks that form from lava that cools at or above the surface
examples of intrusive textures
pegmatitic
phaneritic
porphyritic
examples of extrusive textures
aphanitic porphyritic glassy vesicular fragmental/pyroclastic
pegmatitic texture
very large crystals (some may be >2 cm. in size)
intrusive texture
magma contained large amounts of fluid (water or CO2)
if a number of the crystals are the size of two finger widths, then the rock can be classified as pegmatitic
aphantic texture
fine grained
mineral grains are too SMALL to be see with the unaided eye
extrusive texture
lava cooled relatively quickly + crystals do not have to grow very large
porphyritic texture
often a mixture of fine + coarse grained
2 different (at least) sized mineral grains
intrusive/extrusive textures
magma/lava cooled at different rates resulting in crystals of different sizes
phenocrysts + groundmass
phenocrysts
longer crystals that cooled before the rest of the rock
groundmass
smaller crystals that formed as the rest of the magma cooled
glassy texture
no mineral grains to be seen
extrusive textures
lava cooled so quickly that no minerals could form
will most likely have felsic composition
fragmental (pyroclastic)
rock made up of fragments of volcanic glass, mineral crystals, or lithic (rock) fragments. much of the rock is ash
extrusive
usually associated with violent volcanic eruption
intermediate
Minerals: Na/Ca- Plagioclase Feldspar, Biotite, Amphibole (Hornblende)
Color: Medium to Dark Gray
SiO2 Content: Intermediate
ultramafic
Will not see in lab. Rare on Earth’s Surface
makes up the Earth’s surface
Minerals: Ca-Plagioclase, Pyroxene (Enstatite), Olivine
Usually comprised of over 80% of one of the above minerals.
Color Varies based on mineral composition.
three types of volcanoes and examples of each
shield: ex. Marina Coa
cindercone: ex. Capulin Volcano, New Mexico
stratovolcano (composite): ex. Mt. Saint Helens
shield volcano
curved, with curve facing the sky/convex
typically not as dangerous?
very wide + large
usually composed of MAFIC material
cindercone volcano
much smaller, but can grow very quickly
only about 1000 feet high
usually composed of MAFIC material
stratovolcanoes (composite)
medium in size
only a few 1000 feet high; typically 5-6,000
usually medium gray
usually composed of INTERMEDIATE material
EXPLOSIVE ERUPTIONS
subduction zones
felsic rocks always form here
intermediate
two types of weathering
physical/mechanical
chemical
chemical or organic texture characteristics
compromised of accumulations of shells., precipitated minerals, + other chemical sediments
textures are related to various appearances
- crystalline + microcrystalline
- fossiliferous + microfossiliferous
- oolitic
- carbonaceous
examples of detrital textures
5
angular/coarse-grained
rounded grained
medium grained
fine grained (silt-sized)
very fine grained
examples of chemical textures
crystalline
microcrystalline
fossiliferous
microfossiliferous
oolitic
example of organic texture
carbonaceous
(SIZE) coarse-grained/(SHAPE) angular characteristics
detrital
gravel-sized
grains are larger than 2 mm in size
little to no rounding on grains
*just like taking a hammer to a rock + gluing the pieces together
rounded grained characteristics
SHAPE
detrital
gravel-sized
grains are larger than 2 mm in size
grains show considerable rounding; no sharp angles
very fine grained
SIZE
detrital
clay-sized grains
smaller than 1/256 mm
will feel smooth to skin AND fingernail
both a size and type of mineral
microcrystalline texture
chemical
crystals too small to see with eye
composed of clay-sized chemical sediments
either composed of quartz or calcite
fossiliferous
chemical
compromised of either whole or broken fossils, large enough to see
fossils will be made of calcite
microfossiliferous
chemical
compromised of fossils to small to see w/ eye
will have powdery feel
composed of calcite
carbonaceous texture
organic
compromised of carbon- not actually made of minerals
may have glassy or blocky appearance
two depositional environments of sedimentary rocks
terrestrial + marine
terrestrial environment characteristics
gravels
rusty red colors
salt deposits
carbonaceous material or plant fossils
marine environment characteristics
greens, blacks, tans, browns
UNLESS it has salt
any rock made of calcite
(crystalline, microcrystalline, fossiliferous, microfossiliferous, oolitic)
microcrystalline quartz, regardless of color
what makes a rock metamorphic?
harder/denser/heavier than igneous + sedimentary rocks
likely to possess foliation
rocks more brittle (if fine grained like shale, will be more brittle than shale)
may possess a “sheen” due to foliation
may have grains that are flattened or “oval” shaped because of pressure lack fossils
usually lack the granular cemented nature of sedimentary– more likely to have interlocking crystals. but crystals may be aligned
examples of metamorphic rock
talc chlorite saturolite garnet kyanite
sheen vs. no-sheen
sheen: a soft luster on a surface
layered foliation
in metamorphic rocks, is common in rocks of low to middle grades of alteration
banded foliation
essentially always related to high intensity alteration and found almost exclusively in high grade metamorphic rocks
foliated textures
will have foliated layers or foliation bands
fine-grained
fine-grained w/ sheen
coarse grained
non-foliated textures
will not have foliated layers or bands
fine-grained
coarse-grained
glassy/blocky
metamorphic grade
only applied to foliated rocks
different intensities of metamorphism
when heat, pressure, + chemical action alter the rocks
low metamorphic grade
fine grained/ fine w/ sheen
layered foliation
increase in crystal size with increasing metamorphism
suggests that rocks with smaller/finer grains have undergone less intense alteration
minerals found in metamorphic rocks
talc garnet (sometimes igneous) chlorite (green) staturolite aluminosilicates
what are the aluminosilicates?
sillimonite
andalusite
kyanite (blue)
important changes in metamorphic rocks
change in grain size (larger)
change in grain orientation
change in rock mineralogy
change in rock density
medium grade in met. rocks
coarse grained
layered foliation
high grade in met. rocks
coarse grained
banded foliation
foliated
(very) fine grained
fine grained w/ sheen
coarse grained- medium
coarse grained- high
non-foliated
crystalline
- quartz= scratch glass
- dolomite/calcites- size
glassy/greasy
-carbon
