Rocks

Tenacity = resistance of a mineral to breakage

Malleability = property to break into fragments

Sectility = property to be cut into thin shavings

Flexibility = ability to be bent but does not regain its original shape after removing the stress

Elasticity = property to be bent and regain its original shape after stress is removed

ROCKS

Petrology = study of rocks

I.                    IGNEOUS ROCKS = rocks formed by solidification of magma or lava materials

Types of Igneous Rocks

1.       Volcanic (extrusive)

=originated from lava

=fast rate of cooling

=small sized mineral grains

=fine rock texture (Aphanitic)

Extrusive Igneous Rocks = affected by viscosity (resistance to flow)

Factors Affecting Viscosity

a.       Temperature of lava

=Lava T>>Solidification T, less viscous

b.      Silica Content of lava

Maffic = low silica (~50%), flows easily, dark colored

Felsic = high silica (>65%), flows sluggishly, light colored

Texture of Extrusive Igneous Rock

a.       Aphanitic

b.      Obsidian = volcanic glass

c.       Porphorytic = large crystals enclosed in a matrix of much finer-grained minerals

d.      Vesicular = holes are trapped in rock when lava solidifies while gas is bubbling through it

e.      Pumise = Cooled viscous lava where the gas can’t escape easily, and lava is churned into froth

2.       Plutonic (intrusive)

=from lava

=slow rate of cooling

=large sized mineral grains

=coarse rock texture (Phaneritic)

Intrusive Igneous Rock

a.       Shallow intrusive rocks

i.                     Volcanic neck = formed from magma that solidified within the throat of volcano

ii.                   Dike = tabular, disconcordant (body not parallel to any layering in the country rock)

iii.                  Sill = tabular, concordant (body parallel to any layering in the country rock)

iv.                 Laccolith = concordant with thick central portion and domes upward like a mushroom

b.      Deep intrusive rocks

i.                     Pluton = crystallized at considerable depth, irregular in shape

ii.                   Stock = small disconcordant pluton wit an outcrop area of less than 100 sq. km.

iii.                  Batholith = large disconcordant pluton with an outcrop area greater than 100 sq. km.

Weathering = mechanical disintegration and chemical decomposition upon exposure to surface conditions

= very slow process

= disintegration of rock formations

a.       Physical Weathering = fragmentation of rocks without change in its mineral composition

Factors => frost wedging, plants and animals, salt crystals, pressure release, wind, wave action, abrasion, moving glaciers

b.      Chemical Weathering = Chemical decomposition of rocks

Factors => water (hydrolysis), oxygen, acids

Sediments = product of weathering

                = sometimes referred to as regolith

Agents of Sediment Transportation

                =gravity, run-off, rivers and streams, wind, waves, glacial ice

Traction = process of transporting coarse sediments along the bottom of stream by rolling/sliding

Saltation = movement of sediment along of series of leaps

Rounding = grinding away of sharp edges and corners of rock fragments during transportation

Sorting = process in which sediment grains are selected and separated according to grain size, grain shape or specific gravity

Deposition = when material settles or comes to rest

                = accumulation of chemical or organic sediments

II.                  SEDIMENTARY ROCKS = formed by lithification of sediments

Sediment Particles

>256 mm = Boulder

64-256 mm = Cobble

2-64 mm = Pebble

0.02-2 mm = Sand

0.002-0.02 mm = Silt

<0.002 mm = Clay

Boulder + cobble + pebble = gravel

Silt + clay = mud

Lithification = group of processes that convert loose sediments into sedimentary rocks

a.       Compaction = packing together of loose grains tightly

b.      Cementation = precipitation of cement around sediment grains binding them into a firm rock

c.       Crystallization = solidification of minerals form solution

Types of Sedimentary Rocks

a.       Clastic = formed from lithification of sediments that are fragments of pre-existing rocks

i.                     Breccia = coarse-grained formed by cementation or coarse, angular fragments of rubble

ii.                   Conglomerate = coarse-grained formed by cementation of rounded gravel

iii.                  Sandstone = coarse-grained formed by cementation of sand grains

iv.                 Shale = fine-grained formed by cementation of both silt and clay

v.                   Mudstone = fine-grained formed by cementation of clay

vi.                 Siltstone = fine-grained from silt

b.      Organic = rocks that accumulate from the remains of organisms

i.                     Coquina = cementation of shells that accumulated on the sea floor

ii.                   Limestone = formed from coral reefs

c.       Chemical = from chemical precipitation

i.                     Evaporites = from crystals that precipitate during evaporation of sea or saline water

d.      Others

i.                     Chert = hard, compact, fine grained formed entirely from silica

ii.                   Coal = from solidification of plant materials

Sedimentary Structures

a.       Cross bed = series of thin, inclined layers within a larger bed of rock

b.      Graded bed = layer in which sizes vary gradually from coarse grains at the bottom of the bed to progressively finer grains toward the top

c.       Mud cracks = polygonal patterns of cracks formed in very fine-grained sediment as it dries

d.      Ripple marks = small ridges on the surface of a sediment layer by moving wind of water

e.      Fossils = traces of plants or animals preserved in rock

Bedding = series of visible layers within the rock

3.       METAMORPHIC ROCKS

Metamorphism = solid-state transformation of pre-existing rock into texturally or mineralogically distinct new rock as a result of high temperature, high pressure or both

a.       Contact (Thermal) Metamorphism = Temperature as dominant factor

= non-foliated rocks

= heat comes from intruding magma

b.      Regional (Dynamothermal) Metamorphism = High Temp and pressure

= deformed mountains

= large regions in continents

c.       Progressive Metamorphism = progressively greater T and P act on a rock with increasing depth in the earth’s crust

Factors Affecting Characteristics of Metamorphic Rocks

a.       Parent Rock = based on chemical composition

b.      Temperature = takes place above 200^OC

c.       Pressure

1.       Confining pressure = pressure applied equally on all surfaces of a body

2.       Directed pressure = pressure applied unequally on the surface of the body

i.                     Compressive Direct Pressure = squeezing pressure on both sides

= flattens object perpendicular to applied pressure

ii.                   Shearing Directed Pressure = parts of a body move or slide to one another

= flattens object parallel to the forces exerted

d.      Foliation = parallel arrangement of the textural or structural features of rocks

1.       Foliated

i.                     Slate = fine-grained rock that splits easily along flat parallel planes

ii.                   Schist = fine-grained with visible platy or needle-like structures

iii.                  Gneiss = rock consisting of light and dark mineral layers

2.       Non-Foliated

i.                     Phyllite = rock in which newly formed micas are larger than slate but can’t be seen by the naked eye

ii.                   Migmatite = mixed igneous and metamorphic rocks

iii.                  Marble = derived from limestone

e.      Fluids

f.        Time