RocksRocks

GEOG 3251 Mountain GeographyGEOG 3251 Mountain Geography

summer term B 2010summer term B 2010

Rock cycle

Definition & classificationDefinition & classification

• Rock = a naturally occurring aggregate of minerals and/or mineraloids.

• Classification: mineral and chemical composition; the texture of the constituent particles processes that formed them.

Types of rocks

igneous sedimentary metamorphic

Igneous rocksIgneous rocks

Formed from molten magma (latin ignis = "fire")

2 types: intrusive: magma cools and crystallises slowly

within the Earth's crust extrusive: magma reaches the surface either as

lava or fragmental ejecta.

Classification based on mode of Classification based on mode of occurrenceoccurrence

CompositionMode of occurrence Acid Intermediate Basic Ultrabasic

Intrusive Granite Diorite Gabbro PeridotiteExtrusive Rhyolite Andesite Basalt

Based on compositionBased on composition

FELSIC ROCKS: texture

IntrusiveExtrusive

Muyextrusive

Granite Rhyolite Obsidian

coarser finer

Yosemite Valley: El CapitanYosemite Valley: El Capitan

Intrusive: slow cooling, large texture

ARROWHEADSARROWHEADS

Extrusive: fast cooling, fine texture Obsidian

Igneous Rock TypesIgneous Rock Types

Figure 11.7

Sedimentary rocksSedimentary rocks

• Two ways of forming:– from overburden pressure as particles of

sediment are deposited out of air, ice;

– chemical precipitates (water flows carrying the particles in suspension), eg. carbonate-rich sediments

What makes the Flatirons so What makes the Flatirons so good for climbing?good for climbing?

Type of rock?

•Sandstone •conglomerate

-large particles-good handholds

LimestoneLimestone(Ca CO3)(Ca CO3)• Piatra

Craiului, Carpathians (Romania)

• Karst landscape

Limestone cavesLimestone caves

Metamorphic rocksMetamorphic rocks

• formed by subjecting any rock type (including previously-formed metamorphic rock) to different temperature and pressure conditions than those in which the original rock was formed

Metamorphic rocksMetamorphic rocks

• Foliated: stress that deforms the rock in one plane, e.g. slate is a foliated metamorphic rock, originating from shale.

• Non-foliated: do not have planar patterns of stress; rocks that were subjected to uniform pressure from all

SLATESLATE

Because slate easily flakes, it’s ideal forFloors, roofs, blackboards.

GNEISSGNEISS

Gneiss is characterized by a banded or foliated pattern.Granite is a precursor rock to gneiss

Stress vs.strainStress vs.strain

• Stress = force per unit area

• Strain = amount of deformation an object experiences compared to its original size and shape– Compression: Longitudinal strain that

shortens an object. – Tension: Longitudinal strain that lengthens an

object.

Behavior of MaterialsBehavior of Materials

• Elastic – Material deforms under stress but returns to its

original size and shape when the stress is released.

• Plastic – Material does not flow until a threshold stress has

been exceeded.

• Brittle – Material deforms by fracturing. Glass is brittle.

Rocks typically brittle at low temps and pressures.

How do rocks behave when subjected to How do rocks behave when subjected to stress?stress?

FoldingFolding

FaultingFaulting