Earth science unit 1 rocks and minerals

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

Earth Science Unit 1.3

Rocks & Minerals

• EIGHT ELEMENTS MAKE UP MOST OF

ALL MINERALS ON THE EARTH

– Elements combine to form Minerals

• LISTED IN ORDER OF ABUNDANCE

PERIODIC TABLE OF ELEMENTS

• BUILDING BLOCKS FOR ROCKS

• DEFINITION:

– naturally occurring, inorganic solids,

consisting of specific chemical elements, and

a definite atomic array

• 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

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

• 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

CRYSTALS FORM; SILICA-RICH;

SOLIDIFIED FROM ‘GASSY’ LAVA

• PYROCLASTIC ROCKS

– TUFF: VOLCANIC-EXTRUSIVE;

SEDIMENTARY ROCKS

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

SEDIMENTARY PROCESSES

• 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

METAMORPHIC ROCKS

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

DATING - RELATIVE

different places

formed at same time, under same circumstances

sediment

– fossil remains preserved in the layers of sedimentary rock -fossils

nearer the bottom (in older rock) are more unlike -those near the top

species succeed one another in a definite and recognizable order

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

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