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Rock types
IgneousSedimentaryMetamorphic
Differences in the rock textures
• Igneous – isometric
Differences in the rock textures
• Sedimentary rocks have layers, bedding, strata
Differences in the rock textures
• Metamorphic rocks – are banded, and foliated
metamorphic rocks
• Re crystallization of sedimentary or igneous rocks or even other metamorphic rocks
• In solid state (not liquid)
Metamorphism
• Due to:– High pressure– High temperature – Liquid in pores
Metamorphic temperatures
• Lower boundary – ca 150 Celcius• Upper boundary – ca 1200 Celcius – Above this
temperature the rock mass will melt and form igneous rocks
Result of metamorphism
• new minerals grow• minerals deform and rotate• re crystallization of course minerals• rocks become either:
– stronger but more brittle– or– weaker and anisotropic
?What is the difference between metamorphism, diagenesis and
chemical weathering?
• metamorphism – entails high temperature and high pressure
• diagenesis – entails a bonding and hardening of a sediment relatively near the earths surface
• weathering – entails the disruption and alteration of a solid rock at or near the earth surface
high pressure
Thin section of mica schist
Types of metamorphic rocks
• Regionala metamorphism - high pressure
• Contact metamorphism – high temperature due to igneous intrusion
Regionala metamorphism
Contact metamorf
Contact metamorphism
Textur
• Foliated Foliated – preferred direction of minerals or banding
• Non foliated Non foliated – no preferred direction
metamorphic textures
mosaic texturemosaic texture – interlocking equigranular grains (fig 8.1)
porphoblstic textureporphoblstic texture – larger minerals in a fine matrix (fig 8.2)
folitationfolitation – anisotropy, strong directional structure which effects the properties of the rock so they are different in different directions
Foliation types
• fracture cleavagefracture cleavage – strong rock between fractures, evenly spaced, low grade metamorphism
• slaty cleavageslaty cleavage – parallel to mineral plates, often mica• bedding cleavage – when slaty cleavage coincides with
bedding• schistosityschistosity – is foliation developed by non-random
orientation of macroscopic minerals– lepidoblastic schistositylepidoblastic schistosity – flat mineral plates parallel
to on another– nemotablastic schistositynemotablastic schistosity – elongate minerals in one
plane but not parallel to one another in the plane
Foliation types
• fracture cleavagefracture cleavage – strong rock between fractures, evenly spaced, low grade metamorphism
• slaty cleavageslaty cleavage – parallel to mineral plates, often mica• bedding cleavage – when slaty cleavage coincides with
bedding• schistosityschistosity – is foliation developed by non-random
orientation of macroscopic minerals– lepidoblastic schistositylepidoblastic schistosity – flat mineral plates parallel
to on another– nemotablastic schistositynemotablastic schistosity – elongate minerals in one
plane but not parallel to one another in the plane
Foliation types
• fracture cleavagefracture cleavage – strong rock between fractures, evenly spaced, low grade metamorphism
• slaty cleavageslaty cleavage – parallel to mineral plates, often mica• bedding cleavage – when slaty cleavage coincides with
bedding• schistosityschistosity – is foliation developed by non-random
orientation of macroscopic minerals– lepidoblastic schistositylepidoblastic schistosity – flat mineral plates parallel
to on another– nemotablastic schistositynemotablastic schistosity – elongate minerals in one
plane but not parallel to one another in the plane
Preferred directions
banding and other structures
• bands bands – segregation of different minerals in distinct bands• augenaugen – german for eye – refers to the growth
porphyroblasts, large crystals, in the otherwise finer matrix around which the banding is bent so an eye shape is formed
• boudinage boudinage –French for sausage – is a term for a structure where one layer, which is more brittle than the surrounding layers, is broken into segments around which the other more plastic rock fill in the voids. This forms a series of boudin. (fig 8.4)
• lineations lineations – a linear structure, deferrers from foliation in that it is a sub texture of the main metamorphic texture. All linear structure are oriented parallel
banding and other structures
• bands bands – segregation of different minerals in distinct bands• augenaugen – german for eye – refers to the growth
porphyroblasts, large crystals, in the otherwise finer matrix around which the banding is bent so an eye shape is formed
• boudinage boudinage –French for sausage – is a term for a structure where one layer, which is more brittle than the surrounding layers, is broken into segments around which the other more plastic rock fill in the voids. This forms a series of boudin. (fig 8.4)
• lineations lineations – a linear structure, deferrers from foliation in that it is a sub texture of the main metamorphic texture. All linear structure are oriented parallel
banding and other structures
• bands bands – segregation of different minerals in distinct bands• augenaugen – german for eye – refers to the growth
porphyroblasts, large crystals, in the otherwise finer matrix around which the banding is bent so an eye shape is formed
• boudinage boudinage –French for sausage – is a term for a structure where one layer, which is more brittle than the surrounding layers, is broken into segments around which the other more plastic rock fill in the voids. This forms a series of boudin. (fig 8.4)
• lineations lineations – a linear structure, deferrers from foliation in that it is a sub texture of the main metamorphic texture. All linear structure are oriented parallel
banding and other structures
• bands bands – segregation of different minerals in distinct bands• augenaugen – german for eye – refers to the growth
porphyroblasts, large crystals, in the otherwise finer matrix around which the banding is bent so an eye shape is formed
• boudinage boudinage –French for sausage – is a term for a structure where one layer, which is more brittle than the surrounding layers, is broken into segments around which the other more plastic rock fill in the voids. This forms a series of boudin. (fig 8.4)
• lineations lineations – a linear structure, deferrers from foliation in that it is a sub texture of the main metamorphic texture. All linear structure are oriented parallel
Most common metamorphic rock types
ROCK NAME
TYPE PARENT
ROCK CHARACTERISTICS
SLATE foliated shales and
muds prominant splitting surfaces
SCHIST foliated fine grained
rocks mica minerals, often crinkled or wavy
GNEISS foliated coarse grained
rocks dark and light bands or layers of aligned
minerals
QUARTZITE non-
foliated sandstone
interlocking almost fused quartz grains, little or no porosity
MARBLE non-
foliated limestone
interlocking, often coarse, calcite crystals, little or no porosity
Metamorphic grade
• Pressure and temperature together results in changes such as the growth of minerals and textures
• Indicator minerals – show which temperature and pressure the rock has undergone
Indication minerals
Mineral associations - facies
mineral changes
illite to muscovite chlorite enlarged calcite with the clay to epidote muscovite and chlorite to biotite biotite to garnet or sillimanite
rock names –
starting with shales and mudstones slate phyllite mica schist gneiss
bergarts namn –
börja med lerskiffer skiffer (no difference) fyllit glimmerskiffer gneiss
clorite and epidote common
starting with ultra basic rocks green schist garnet schist amphibolite
igneous basiska bergarter grönskiffer grantskiffer amfibolit
epidote and chlorite common
volcanic rocks metavolcanics greenstone
volcaniska bergarter leptit, hälleflinta grönsten
dolomite to calcite and brucite, tremolite wollastonite garnet
limestone marble calc-schist skarn
kalksten marmor kalkskiffer skarn
Weathering of metamorphic rocks
• Wide range of weathering products– gneiss, granulites and other quartz rich rocks – sandy
residual soils smilar to granitic soils– slate and phyllite – miaceous, silty residual soils– marble – red clay – foliation – bladed outcrops tombstone – rock head
separated by completely decomposed material– banded – banded saprolite with clay between bands– weathering depth – dependent upon spacing of
fractures, typical 6 to 24 m depth
joints
• sets of 4 or more are common• joints coated with clay or silt• intersections isolate potentially
removable blocks (fig 8.12)
foliation shears
• persistent shear zones parallel to the plane of foliation, cm to m in size
• tensile and shear strengths are considerably less than in all other directions, strength anisotropy
• characterized by finely fractured or crushed rock
two end members – impervious impervious - plastic clay seam common, alteration to
chlorite or kaolinite replacing feldspars and biotite– pervious pervious - shear zone of crushed rock
Engineering and metamorphic rocks
Exploration
• irregular extent• recognition of rock types• foliation directions important• weathering zones detection• geophysical methods• drilling (difficult in quartzite)
slope stability
Landslides• common due to extremely weak
shear strengths of platy minerals• valley form asymetrical
– gentle - dip slip slopes – slab slide– steep – slopes with creep, toppling,
landslides
surface excavation
• blasting often required• landslide risk – block theory• slab slides• toppling
foundations
• fresh rock – usually good• weathered rock
– compressible sandy silty soil
– pile difficult
• saprolite – protect from drying – loose of fabric
• slope failures – common along the plain of foliation
Case histories
• Several in the book• Read – do you understand the
descriptions of the rock and their physical nature?