RocksRocks
GEOG 3251 Mountain GeographyGEOG 3251 Mountain Geography
summer term B 2010summer term B 2010
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.
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
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
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
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.