Transcript Rocks and Minerals

Earth Science Unit 1.3
Rocks & Minerals
ELEMENTS
• EIGHT ELEMENTS MAKE UP MOST OF
ALL MINERALS ON THE EARTH
– Elements combine to form Minerals
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LISTED IN ORDER OF ABUNDANCE
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OXYGEN (O)
SILICON (Si)
ALUMINIUM (Al)
IRON (Fe)
CALCIUM (Ca)
POTASSIUM (K)
SODIUM (Na)
MAGNESIUM (Mg)
PERIODIC TABLE OF ELEMENTS
MINERALS
• BUILDING BLOCKS FOR ROCKS
• DEFINITION:
– naturally occurring, inorganic solids,
consisting of specific chemical elements, and
a definite atomic array
• CRYSTALLINE STRUCTURE – ‘CRYSTAL’
MINERALS
• MINERALS: TWO CATEGORIES
– SILICATES – CONTAIN SILICON & OXYGEN
MOLECULES (SiO)
– NON-SILICATES (NO SiO)
NON-SILICATE MINERALS
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Make up 5% of Earth’s crust
Native metals: gold, silver, copper
Carbonates: calcite (used in cement)
Oxides: hematite (iron ores)
Sulfides: galena (lead ores)
Sulfates: gypsum (used in plaster)
SILICATE MINERALS
• Make up 90-95% of the Earth’s Crust
• Dominant component of most rocks,
include:
– QUARTZ (SiO2)
– FELDSPARS
– MICAS
ROCKS
• AGGREGATIONS OF 2 OR MORE
MINERALS
– Same or different minerals combine together
• THREE CATEGORIES
– IGNEOUS
– SEDIMENTARY
– METAMORPHIC
IGNEOUS ROCKS
• FORMED FROM COOLED, SOLIDIFIED
MOLTEN MATERIAL, AT OR BELOW THE
SURFACE
• PLUTONIC – INTRUSIVE: COOLED
BELOW SURFACE AT GREAT DEPTHS
• VOLCANIC – EXTRUSIVE: COOLED AT
OR NEAR THE SURFACE THROUGH
VOLCANIC ERUPTIONS
IDENTIFICATION OF IGNEOUS
ROCKS
• IDENTIFICATION PROCESSES:
– TEXTURE:
• Size, shape and manner of growth of
individual crystals
– MINERAL COMPOSITION
• Based on SiO content
COMMON IGNEOUS ROCKS
• GRANITE:
PLUTONIC-INTRUSIVE; PHANERITIC TEXTURE; FELSIC
MINERAL COMPOSITION
• RHYOLITE: VOLCANIC-EXTRUSIVE; APHANETIC TEXTURE;
FELSIC MINERAL COMPOSITION
• DIORITE:
PLUTONIC-INTRUSIVE; PHANERITIC TEXTURE;
INTERMEDIATE MINERAL COMPOSITION
• ANDESITE:
VOLCANIC-EXTRUSIVE; APHANETIC TEXTURE;
INTERMEDIATE MINERAL COMPOSITION
• GABBRO: PLUTONIC-INTRUSIVE; PHANERITIC TEXTURE; MAFIC
MINERAL COMPSITION
• BASALT: VOLCANIC-EXTRUSIVE; APHANETIC TEXTURE; MAFIC
MINERAL COMPOSITION
OTHER IGNEOUS ROCKS
• VOLCANIC GLASS:
– OBSIDIAN: VOLCANIC-EXTRUSIVE; NO
CRYSTALS FORM; SILICA-RICH, COOLED
INSTANEOUSLY
– PUMICE: VOLCANIC-EXTRUSIVE; NO
CRYSTALS FORM; SILICA-RICH;
SOLIDIFIED FROM ‘GASSY’ LAVA
• PYROCLASTIC ROCKS
– TUFF: VOLCANIC-EXTRUSIVE;
SOLIDIFIED ‘WELDED’ ASH
SEDIMENTARY ROCKS
• Weathering processes break rock
into pieces, sediment, ready for
transportation deposition burial
lithification into new rocks.
CLASSIFYING SEDIMENTARY ROCKS
THREE SOURCES
• Detrital (or clastic) sediment is composed of
transported solid fragments (or detritus) of pre-existing
igneous, sedimentary or metamorphic rocks
• Chemical sediment forms from previously dissolved
minerals that either precipitated from solution in water ,
or were extracted from water by living organisms
• Organic sedimentary rock consisting mainly of plant
remains
SEDIMENTARY ENVIRONMENTS
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Lakes
Lagoons
Rivers
Ocean bottoms
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Estuaries
Salt Flats
Playas
Glacial environments
SEDIMENTARY PROCESSES
• LITHIFICATION:
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As sediment is buried several kilometers beneath the surface, heated from
below, pressure from overlying layers and chemically-active water
converts the loose sediment into solid sedimentary rock
• Compaction - volume of a sediment is reduced by
application of pressure
• Cementation - sediment grains are bound to each other
by materials originally dissolved during chemical
weathering of preexisting rocks
– typical chemicals include silica and calcium carbonate.
METAMORPHIC ROCKS
• METAMORPHISM : process by which
conditions within the Earth alter the
mineral content and structure of any rock,
igneous, sedimentary or metamorphic,
without melting it.
• Metamorphism occurs when heat and
pressure exceed certain levels,
destabilizing the minerals in rocks...but not
enough to cause melting
Time for a break…
GEOLOGIC TIME AND DATING
• Four basic principles
– Principle of Original Horizontality
– Beds of sediment deposited in water formed as horizontal or
nearly horizontal layers.
– Principle of Superposition
– Within a sequence of undisturbed sedimentary or volcanic
rocks, the layers get younger going from bottom to top.
– Lateral Continuity
– An original sedimentary layer extends laterally until it tapers or
thins at its edges
– Cross-cutting Relationships
– A disrupted pattern is older than the cause of the disruption.
DATING - RELATIVE
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Physical Continuity
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Similarity of Rock Types
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Physically tracing the course of a rock unit to correlate rocks between two
different places
Correlation of two regions by assumption that similar rock types in two regions
formed at same time, under same circumstances
Correlation by Fossils
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Plants and animals that lived at the time rock formed were buried by
sediment
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fossil remains preserved in the layers of sedimentary rock -fossils
nearer the bottom (in older rock) are more unlike -those near the top
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Observations formalized into Principle of Faunal Succession – fossil
species succeed one another in a definite and recognizable order.
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Index Fossil – a fossil from a short-lived, geographically widespread
species known to exist during a specific period of geologic time.
ABSOLUTE DATING DENDROCHRONOLGY
• Using annual growth rings of trees
• Dates for trees now extending back more
than 9,000 years.
• Bristlecone Pine, White Mountains, CA (pinus
longaeva) provides a continuous time scale for last
9,000 years (to 7000 B.C)
• Provides calibration of radiocarbon dates
over most of the last 10,000 years
(Holocene epoch)
DENDROCHRONOLOGY
ABSOLUTE DATING
VARVE CHRONOLOGY
• Varves are parallel strata deposited in deep
ocean floors or lake floors
• A pair of sedimentary layers are deposited
during seasonal cycle of a single year
– Laminae (similar to annual growth rings in trees)
record climatic conditions in a lake or large water
body from year to year
• Cores extracted from sea floor or lake floor are
used to date back several million years to 200
million years
VARVE CHRONOLOGY
DATING - ABSOLUTE
• Radiometric dating – based on radioactive
decay of ‘isotopes’
• Decay rate can be quantified because it
occurs at a constant rate for each known
isotope – “half-life” from parent isotope to
stable ‘daughter’ isotope
• Measuring ratio of parent to daughter
isotopes determines absolute ages of
some rocks.
ABSOLUTE DATING ISOTOPES
• URANIUM–LEAD (U238–Pb206)
– Half-life: 4.5 billion years
– Dating range: 10 million – 4.6 billion years
• URANIUM–LEAD (U235-Pb207)
– Half-life: 713 million years
– Dating Range: 10 million – 4.6 billion years
• POTASSIUM-ARGON (K40-Ar40)
– Half-life: 1.3 billion years
– Dating Range: 100,000 – 4.6 billion years
• CARBON-14 (C14-N14)
– Half-life: 5730 years
– Dating Range: 100 – 100,000 years