Earth Science Unit 1.3 Rocks & Minerals

ELEMENTS 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 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 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 THREE CATEGORIES 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: PYROCLASTIC ROCKS 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 Lakes Lagoons Rivers Ocean bottoms Estuaries Salt Flats Playas Glacial environments

SEDIMENTARY 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 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 Physical Continuity Similarity of Rock Types 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 - 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