Rocks GEOG 3251 Mountain Geography summer term B

Rocks GEOG 3251 Mountain Geography summer term B 2010

Rock cycle

Definition & 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 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 occurrence

Based on composition

FELSIC ROCKS: texture Intrusive Granite coarser Extrusive Rhyolite Muy extrusive Obsidian finer

Yosemite Valley: El Capitan Intrusive: slow cooling, large texture

ARROWHEADS Extrusive: fast cooling, fine texture Obsidian

Igneous Rock Types Figure 11. 7

Sedimentary 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 good for climbing? Type of rock? • Sandstone • conglomerate -large particles -good handholds

Limestone (Ca CO 3) • Piatra Craiului, Carpathians (Romania) • Karst landscape

Limestone caves

Metamorphic 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 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

SLATE Because slate easily flakes, it’s ideal for Floors, roofs, blackboards.

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

Stress 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 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 stress?

Folding

Faulting