01 - Rock Classification Flashcards
Definition
Rock
naturally occurring aggregates of one (monomineralic) or more minerals (polymineralic).
Three major rock groups
Igneous rocks -> magmatites
Metamorphic rocks -> metamorphites
Sedimentary rocks -> sediments
Three main processes of rock cycle
- Erosion & sedimentation
- Melting & recrystallization
- Sink & recrystallization
Igneous rocks:
three types by occurence and position in crust
plutonic
volcanic
subvolcanic
Igneous rocks:
classification according to chemical / mineralogical composition
distingluishes .. (4)
- felsic or silicic rocks (granite, rhyolite) -> acid
- intermediate rocks (granodiorite, diorite, dacite, andesite)
- mafic rocks (basalt, gabbro) -> basic
- ultramafic rocks (peridotite, dunite)
Igneous rocks:
Streckeisen in Exercise 1
Mafic & Ultramafic clasification -> Bilder angucken
TAS
Streckeisen in Exercise 1
Mafic & Ultramafic clasification -> Bilder angucken
TAS
Metamorphic rocks:
classification … (4)
- in low, medium, high grade
- in metamorphic facies zones (mineral paragenesis)
- after textures (slate, schist, gneiss, fels)
- after origin (contact-, regional-, subduction-, shock-)
classification in low, medium, high grade:
Sort with increasing metamorphic grade:
- schist
- gneiss
- slate
- blueschist
- phyllite
- migmatite
Low grade:
- slate
- phyllite
Intermediate grade:
- blueschist
- schist
High grade:
- gneiss
- migmatite
in metamorphic facies zones:
name the 3 major types of metamorphic series
- High P/T Series
- Medium P/T Series
- Low P/T Series
in metamorphic facies zones:
- High P/T Series - facies?
Zeolite
- > Blueschist
- > Eclogite
(high increasing P and low increasing T)
in metamorphic facies zones:
- Medium P/T Series - facies?
Zeolite
- > Greenschist
- > Amphibolite
- > Granulite
(increasing P and increasing T)
in metamorphic facies zones:
- Low P/T Series - facies?
Zeolite
- > Hornfels (Ab-Ep -> Hornblende -> Pyroxene)
- > Sanidinite or Granulite
( low increasing pressure and high ingreasing T
Sedimentary rocks:
name the 3 major rock classes
- clastic
- chemical
- organic
Sedimentary rocks - clastic:
formation processes
- erosion, reworking, transportation
- deposition & sedimentation
- compaction and diagenetic processes
Sedimentary rocks - clastic:
what does the physical properties strongly depend on?
(was red marked in lecture)
- Textural properties:
- particel dimensions
- size
- shape
- spatial orientation - mineral composition
- presence and effect of clay minerals
Sedimentary rocks - clastic:
Grain size classification
< 0.002 mm Clay
- 002 - 0.0063 mm Silt
- 0063 - 2.0 mm Sand
- 0 - 63 mm Gravel
> 63 mm Boulder
Sedimentary rocks - clastic:
Q,F,L classification
Q - quartz
F - feldspar
L - lithoclasts
and matrix
< 5% matrix:
- > Quartz arenite (Q)
- > Feldspatic arenite (F,Q)
- > Lithic arenites (L,Q)
5-50% matrix
Wackes
> 50% matrix:
shales/Mudrocks
Sedimentary rocks - clastic:
Shale
mixture of:
clay, silt (some sand) sized particles
Sedimentary rocks - clastic:
Clays - structure
alumosilicates with sheet structure and different stacking combinations:
- tetrahedral unit with central Si-atom and surrounding O
- octahedral unit with central Al and surrounding O atoms and OH groups
Sedimentary rocks - clastic:
Clays - examples
Kaolinite (Al)
Illite (K,Al)
Montmorillonite (Ca,Na,Al,Mg,Fe, H2O-layer )
Chlorite (Mg,Al,Fe)
Sedimentary rocks - clastic:
Clays - how are exchangeable cations measured ?
by cation exchange capacity (CEC)
Smectite/ Montmorillonite HIGH
Kaolinite LOW
Sedimentary rocks - chemical:
Carbonates & Evaporate rocks - Formation
chemical and biochemical precipitation depending on environments:
- typically warm
- shallow
- clear marine water in low latitudes
Sedimentary rocks - chemical:
Carbonates & Evaporate rocks - Sources of secondary porosity
- fracturing
- solution
- chemical replacement
Sedimentary rocks - chemical:
Carbonates - most abundant carbonate minerals
- calcite CaCO3
- dolomite CaMg(CO3)2
also:
- anhydrite
- chert
- quartz
+ accessory (phosphates etc.)
Sedimentary rocks - chemical:
Carbonates - post-depositional processes
dissolution
cementation
recrystallization
dolomitization (increasing porosity)
replacement
Sedimentary rocks - chemical:
Carbonates - Classification after Dunham
(Kendall in slides)
Picture in Lecture:
Mudstone (mud-supported, < 10% grains)
Wackestone (mud-supported, > 10 % grains)
Packstone (grain-supported, with mud)
Grainstone (grain-supported, without mud)
Boundstone (bound at deposition, intergrown, lamination)
Texture includes ..
grain size
size distribution
shape
packing
What does the grain diameter depend on
particles with non-spherical shape depend on technique of determination
1) sieve analysis: minimum cross-sectional axis
2) image or laser scanning: numerical algorithm for representive size distribution
Slide 23: Grain size distribution:
well and poorly sorted
well: mainly one size occur
poorly: wide range of different sizes
Particle size depend on ..
environmental setting
tronsporting agent
length and time during transport
depositional conditions
Phi-scale
phi = -log_2(d)
with d in mm
median grain size
midpoint at d50 (at 50%)
grain sorting S_0
how narrow distribution is:
S_0 = (d25/d75)^1/2
Skewness S_k
symmetry:
S_k = (d25*d75)/d50^2
Sieving analysis:
sediment pass through series of stacked sieve meshes (by agitation)
wet or dry
Sieve catch grains larger than mesh size
fractions were weighted o get percentages relative to whole sample
Atterberg method
by sedimentation or settling
measures rate of sedimentation of particles suspended in liquid
not useful for < 5 mikrometer
Laser diffraction
measures angular dependence of laser light scattered by particles
Stereology
mean intercept length of a sphere
3D interpretation of 2D cross sections
0.667 as fraction of diameter
was Homework
Borehole imaging
- Optical imaging
- Acoustic imaging
- Electrical imaging
Borehole imaging
- Optical imaging
Optical & hyperspectral scanning:
- > downhole scanning
- > core scanning (360 °)
- > 3D Channel Spectral data
CT-scanning
use a x-ray source -> through object and scanned by detector on other side
numelrical agorithm to construct 2D cross section
x-ray attenuation proportional to density
determination of porosity
Classification of rock properties:
direc interest for application (4)
- reservoir properties
(porosity, saturation, permeability) - geochemical properties
(deformation, strength) - mineralogical characteristics
(shale content, fractional min. composition) - content of substances of interest
(ore content)
Classification of rock properties:
measured by geophysical methods
(elastic/seismic, density, electical, nuclear)
Scalar properties
- porosity
- fluid saturation
- density
- nuclear cross-sections
Tensorial properties
- permeability
- deformation modulus
- strength properties
- elastic, electrical, thermal, magnetic properties
Routine core (plug) analysis
- Porosity (photo)
- permeability (CT scan)
- grain density (fluids)
- gamma
Special core analysis
- capillary pressure
- nuclear magnetic resonance
- electrical properties
- acoustic properties
- clay minerals
- specific tests
isotropic anisotropic
homogenious inhomogenious
isotropic-homogeneous: OOO
anisotropic-homogeneous: 000
Isotropic-inhomogenieous: °oO
Anisotropic-inhomogeneous: 0o0
