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ENVIRSC 1G03 Study Guide - Comprehensive Midterm Guide: Iceage, Conchoidal Fracture, Magnetite


Department
Environmental Science
Course Code
ENVIRSC 1G03
Professor
Maureen Padden
Study Guide
Midterm

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McMaster
ENVIRSC 1G03
MIDTERM EXAM
STUDY GUIDE

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ENVIR SC 1G03 (Earth & the Environment) - Dr. Maureen Padden
Textbook Interlude A
A.1) Introduction
1849 gold rush in Sierra Nevada (California) made a few very rich and most very
poor.
Those that didn’t get rich often settled in new towns near the American west coast,
like San Francisco.
Demanded large quantities of east-coast-factory-produced goods. Hard to
transport them, though:
Built a railroad linking the east and west coasts of north America.
1863: transport of 6000 Chinese labourers in terrible conditions (many died of
frostbite, exhaustion, mistimed blasts, landslides, or avalanches).
There are many distinct types of rocks, because they can form in many different
ways and from many different materials.
Rocks provide a historical record of geologic events and give insight into
interactions of components of the Earth system (relationship between rock
type and process of formation).
A.2) What Is a Rock?
Rock: a coherent, naturally occurring solid, consisting of an aggregate of minerals or
(less commonly) of glass.
Specific characteristic definitions:
1) Coherent: rocks hold together, and can only be separated into pieces by
breaking.
Rocks can form cliffs or be carved into sculptures.
A pile of unattached mineral grains is not a rock.
2) Naturally occurring: rocks cannot be manufactured (bricks and concrete aren’t
rocks).
3) Aggregate of minerals / mass of glass: most rocks are an aggregate (collection)
of many mineral grains and/or crystals stuck/grown together.
Some contain only one kind of mineral, some contain several kinds.
Some rocks consist of glass.
Rocks are held together because:
1) Clastic rocks: they are bonded by natural cement (mineral material that
precipitates from water and fills space between grains)
2) Crystalline: they interlock like pieces of a puzzle.
Glassy rocks hold together because they originate as continuous masses (no
separate grains)–glassy grains are welded together while still hot, or
cemented together later.
At Earth’s surface, rock occurs either as broken chunks that have been moved by
falling down slopes or transported by water or wind, or as bedrock still
attached to Earth’s crust.
Outcrop: exposures of bedrock.
May appear as rounded knobs, ledges forming cliffs or ridges, on the face of a
stream cut, or along human-made roadcuts and excavations.
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Bedrock may be completely covered by vegetation, sand, mud, gravel, soil,
water, asphalt, concrete, or buildings and be unfamiliar.
Particularly rare to see bedrock in the midwestern United States, where ice-age
glaciers deposited debris on top of bedrock in the past million years.
A.3) The Basis of Rock Classification
18th century beginnings: attempts to classify rocks sensibly–not all rocks are the
same.
Classification schemes help organize information and remember significant details
about materials or objects.
Also help to recognize similarities and differences between them.
End of 18th century: wide acceptance of modern genetic scheme for rock
classification.
Focuses on the origin (genesis) of rocks.
Genetic Scheme: recognizes three basic
groups of rock:
1) Igneous rocks, formed by freezing
(solidification) of molten rock).
2) Sedimentary rocks, formed either by
cementing together of fragments
(grains) broken off preexisting
rocks; or by precipitation of mineral
crystals out of water solutions at or
near Earth’s surface.
3) Metamorphic rocks, formed when preexisting rocks change character in
response to a change in pressure and temperature conditions.
Occurs in the solid state, doesn’t require melting.
Different rock types form in different geologic settings.
Each of these groups contains many different individual rock types, distinguished by
physical characteristics:
1) Grain size: dimensions of individual “grains” in a rock can be measured in mm
or cm.
Some are so small they can’t be seen with a microscope, some are large enough
to be seen with the naked eye (or are actually quite large).
Grains can be equant (same dimensions in all directions) or inequant
(dimensions are not the same in all directions).
2) Composition: rocks are masses of chemicals; proportions of different chemicals
that make up a particular rock are its composition.
The proportion of chemicals affects the proportion of different minerals that
constitute a rock.
3) Texture: the arrangement of grains in a rock, as grains connect to one another.
Whether inequant grains are aligned parallel to each other.
4) Layering: some rock bodies appear to contain distinct layering, defined by
bands of different compositions or textures, or by the alignment of inequant
grains so they trend parallel to one another.
Different types of layering occur in different kinds of rocks.
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