Download Rock and Rock Materials - Washington State University

Ch. 2, Part-II
Rocks, Rock Materials &
Geologic Structures
Chapter (Section) Objectives
• Review of some of the important mineral and rock types and
their environmental significance
– Relationships between atoms, minerals, rocks, rock materials
– Basic silicate building block(s)
– Properties of rocks & minerals
– Basic rock types, basis for classification,
– Why this stuff is important & the types of information they provide
• Appreciation/significance of geologic structures
– Layering
– Folds
– Faults
– Other structures (joints, dikes/sills, etc.)
•Rock:
– A solid, cohesive aggregate of grains of one or more minerals
•Mineral:
– Naturally occurring crystalline inorganic substance with a definite
chemical composition; element or compound with a systematic
arrangement of atoms / molecular structure (e.g., sulfur, salt,
silicates such as feldspar)
•Crystallinity
– Atomic arrangement imparts specific physical and chemical
properties
•Physical properties of minerals:
– color, hardness, cleavage, specific gravity, streak, etc.
Minerals:
– Systematic groupings of atoms
– e.g., salt (NaCl)
• Relationship between:
–
–
–
–
–
Atoms
Molecules
Minerals
Rocks
Landforms
Basic Silicate Structure:
The silica tetrahedron
Silicate Mineral Structures
Main Rock Forming Minerals
Fewer than 20 minerals account for the bulk of the earth’s
crust: Most are silicates
(See Hand Specimens)
Percent
in Crust
51%
(39)
(12)
12 %
11 %
5%
5%
5%
3%
8%
Mineral (formula)
Igneous
Feldspar (Na, K, Ca) (Al,Si)4 O8
X
Plagioclase (Na, Ca) (Al,Si)4 O8
Alkali feldspar (Na, K) (Al,Si)4 O8
Quartz- SiO2
X
Pyroxene- (Ca, Mg, Fe) Si2 O6
X
AmphiboleX
MicaX
ClayX
Olivine (Mg, Fe)2 Si O4
X
Others (non-silicates)X
halides, sulfates, sulfides, carbonates,
Fe-Ti oxides, phosphates, native elements, etc.)
Sedimentary
Metamorphic
X
X
X
X
X
X
X
X
X
Minor and trace elements: Minor element minerals (sulfides, uranium mins., heavy metals, trace
element substitutions.
Rock Materials & Properties
• Rock materials:
Composed of one or more component minerals having
discrete physical and chemical characteristics
• The physical (e.g., color, hardness) and chemical
characteristics of rocks and rock material reflect the
combined characteristics (properties) of the discrete
component materials (i.e., minerals)
Rock Strength: Stess-Strain Relationships
Three (3) Major Rock Types
1. Igneous
–
Formed from molten material (e.g., lava, granite)
2. Sedimentary (including sediment)
–
Formed from the weathering of other rocks, as
chemical precipitates, or biologic material
(shells)
3. Metamorphic (including hydrothermal rocks
& minerals)
–
Rocks modified/changed by heat and/or pressure
Relationship between Rock
Types and Plate Tectonics
Rock Cycle- Cycle of melting, crystallization, weathering/erosion, transportation,
deposition, sedimentation, deformation ± metamorphism, repeat of crustal materials.
Igneous Rocks
• Definition:
– Rocks formed from high-temperature silicate liquid
(molten) rock material (magma)
[high-temperature  800oC to 1300oC]
• Igneous rock material
– Formed by solidification of molten material
– Usually with the formation of high-temperature minerals
(as crystals) that form from the magma as it cools
Classification of Igneous Rocks
• By Physical Criteria, i.e., grain size
– Cooling rate & where cooling occurs (determines grain
size)
• Chemical Criteria, i.e., Composition
– Mainly by relative amounts of iron (Fe), magnesium
(Mg), silicon (Si), ± water
• Primary Materials
– Material from which magma is formed (mantle, crust)
– Material that is “melted” to form magma
Classification of Igneous Rocks:
By Physical Criteria
• Slow cooling  produces large crystals (minerals)  Coarse-grained rocks
– Example: Granite
– Slow cooling due to intrusive, thermally insulated
emplacement of magma
• Rapid cooling  produces small, or no crystals  Fine-grained rocks
– Example: lava, ash
– Rapid cooling due to “extrusion, i.e., eruption” of magma at
surface
Relationship between Rock
Types and Plate Tectonics
Classification of Igneous Rocks:
By Physical Criteria
Cooling Rate
Rapid
Setting:
- Extrusive, i.e., Volcanic
-Erupted; on the surface or very shallow
Characteristics/Features:
- Crystals: very small or absent
- Rock = Fine-grained or glassy
Further Subdivided By Eruptive Style:
-Explosive (w/ gas, water)
-Non-explosive (Hawiian-type)
Examples:
- Lava
- Ash
Slow
Setting:
- Intrusive (plutonic)
- Deep within the earth
Characteristics/Features:
- Crystals: Large
- Rock = Coarse-grained
Further Subdivided By Depth & Relative Grain-Size:
-Very deep = very slow = very large crystals
-Medium or shallow depth = medium-size crystals
Examples:
- Granite
- Gabbro
Correlations between composition and physical
properties, such as eruptive style of volcanic rocks
• Silica Content
– Si-poor magmas (Hawiian-type) are fluid (low viscosity)
– Si-rich volcanic magmas (St. Helen’s-type) are viscous (sticky)
• Explosiveness
– Explosive eruptions result from Si-rich magmas w/ water, gases
– Explosiveness depends on how well gases and water are
released from the magma
• Lower viscosity, less gas  non-explosive eruptions
• High viscosity + gas  violently explosive eruptions
• So where & why do these types occur??? (more later)
Chemical & Physical Properties of
Igneous Rocks and Plate Tectonics
Sedimentary Rocks
• Rocks form from:
– The mechanical and/or chemical weathering of
other rocks
– Material deposited/precipitated from water via
chemical or biological (organic) processes
Types / Classification of Sedimentary Rocks
1.
2.
3.
4.
Clastic: Formed from the mechanical and/or chemical
weathering of other rock materials
–
Sandstone, shale
–
conglomerate
Chemical: Formed as inorganic precipitates (i.e., water saturated
with respect to chemical compounds)
–
Limestone (Ca-carbonates (caliche)
–
Other salts, e.g., sulfates, hydroxides, halogen salts (e.g., NaCl)
–
Silica
Organic: Formed from (and including) organic material such as:
–
Fossil materials (typically shells, diatoms, etc.); exoskeletons, or endoskeletons of
–
Organic and/or chemical cements (carbonate, silica, phosphates)
aquatic (e.g., marine) organisms
Combinations
–
e.g., Clastic or organic sediment with chemical cement
Clastic Sedimentary Rocks:
Further classified by grain size
Chemical
Sediments
e.g., evaporite
salt deposits
Organic
Sediment
Chalk
Environmental Conditions Indicated From
Sediment and Sedimentary Rocks
• Environment in which they formed, e.g.,
– Marine
• Deep (limestone, shale)
• Shallow (deltas, reefs)
– Terrestrial
• Glacial
• River/stream
• Arid/desert
• Environmental conditions
– Source(s)
– Mode and distance of transport
– Depositional processes, e.g., near-source vs. mature sediment
(coarse sand vs. shale)
Metamorphic Rocks
Formed from other rocks but modified
(e.g.,recrystallized) by heat and/or pressure
• Types
– Foliated (alignment or banding of planar minerals)
• Slate
• Schist
• gneiss
– Non-foliated (no preferrential alignment of minerals)
• Quartzite
• Marble (sometimes foliated)
• Hydrothermal/baked rocks (skarn)
Foliated Metamorphic Rock
Significance of Rock Types to
Environmental Geology
• Type and origin of rocks provide insight into present or past
environmental conditions (e.g., flood deposits, volcanic
mudflows)
• Differences in rock types can have important envirornmental
implications (e.g., strata/layers)
• Physical Properties
– Strength
– Planes of weakness
– Porosity, permeability
• Chemical Properties
– Tendency to dissolve (solubility), leach, or react
Examples
• Limestone:
–
–
–
–
Typically formed in a reef or deep marine setting
Highly stable in arid climates, unstable in wet climates
Poor aquifer material
Highly conducive to formation of ore deposits when
adjacent to igneous magmas or hydrothermal fluids
• Implications for finding them in high mountains?
Examples con’t
• Sandstone
– Formed as near-shore marine and desert environments (w/
noteable differences)
– Moderate strength
– Generally porous and permeable
• Foliated Metamorphic Rocks
– Implies formation under conditions of directed tectonic forces
– Have potential planes of weakness
• Others (See charts/figures)
Relationship between Rock
Types and Plate Tectonics