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?