Post on 30-Mar-2015
Earth Science Unit 1.3Earth Science Unit 1.3Rocks & MineralsRocks & Minerals
ELEMENTSELEMENTS• EIGHT ELEMENTS MAKE UP MOST OF
ALL MINERALS ON THE EARTH– Elements combine to form Minerals
• LISTED IN ORDER OF ABUNDANCE– OXYGEN (O)– SILICON (Si)– ALUMINIUM (Al)– IRON (Fe)– CALCIUM (Ca)– POTASSIUM (K)– SODIUM (Na)– MAGNESIUM (Mg)
PERIODIC TABLE OF ELEMENTSPERIODIC TABLE OF ELEMENTS
MINERALSMINERALS
• BUILDING BLOCKS FOR ROCKS
• DEFINITION:– naturally occurring, inorganic solids,
consisting of specific chemical elements, and a definite atomic array
• CRYSTALLINE STRUCTURE – ‘CRYSTAL’
MINERALSMINERALS
• MINERALS: TWO CATEGORIES
– SILICATES – CONTAIN SILICON & OXYGEN MOLECULES (SiO)
– NON-SILICATES (NO SiO)
NON-SILICATE MINERALSNON-SILICATE MINERALS
• 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 MINERALSSILICATE MINERALS
• Make up 90-95% of the Earth’s Crust
• Dominant component of most rocks, include:– QUARTZ (SiO2)
– FELDSPARS
– MICAS
ROCKSROCKS
• AGGREGATIONS OF 2 OR MORE MINERALS– Same or different minerals combine together
• THREE CATEGORIES– IGNEOUS– SEDIMENTARY– METAMORPHIC
IGNEOUS ROCKSIGNEOUS 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 IDENTIFICATION OF IGNEOUS ROCKSROCKS
• IDENTIFICATION PROCESSES:
– TEXTURE: • Size, shape and manner of growth of
individual crystals
– MINERAL COMPOSITION• Based on SiO content
COMMON IGNEOUS ROCKSCOMMON 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 ROCKSOTHER 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 ROCKSSEDIMENTARY ROCKS
• Weathering processes break rock into pieces, sediment, ready for transportation deposition burial lithification into new rocks.
CLASSIFYING SEDIMENTARY ROCKSCLASSIFYING SEDIMENTARY ROCKSTHREE 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 ENVIRONMENTSSEDIMENTARY ENVIRONMENTS
• Lakes• Lagoons• Rivers• Ocean bottoms
• Estuaries• Salt Flats• Playas• Glacial environments
SEDIMENTARY PROCESSESSEDIMENTARY PROCESSES
• LITHIFICATION:• 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 ROCKSMETAMORPHIC 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…Time for a break…
GEOLOGIC TIME AND DATINGGEOLOGIC 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 - RELATIVEDATING - RELATIVE• Physical Continuity
– Physically tracing the course of a rock unit to correlate rocks between two different places
• Similarity of Rock Types– Correlation of two regions by assumption that similar rock types in two regions
formed at same time, under same circumstances
• Correlation by Fossils– Plants and animals that lived at the time rock formed were buried by
sediment
– fossil remains preserved in the layers of sedimentary rock -fossils nearer the bottom (in older rock) are more unlike -those near the top
– Observations formalized into Principle of Faunal Succession – fossil
species succeed one another in a definite and recognizable order.
– Index Fossil – a fossil from a short-lived, geographically widespread species known to exist during a specific period of geologic time.
ABSOLUTE DATING - ABSOLUTE DATING - DENDROCHRONOLGYDENDROCHRONOLGY
• 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)
DENDROCHRONOLOGYDENDROCHRONOLOGY
ABSOLUTE DATINGABSOLUTE DATINGVARVE CHRONOLOGYVARVE 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 CHRONOLOGYVARVE CHRONOLOGY
DATING - ABSOLUTEDATING - 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 ISOTOPESABSOLUTE 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