1. Earth Science Unit 1.3 Rocks & Minerals

2. 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)

3. PERIODIC TABLE OF ELEMENTS

4. MINERALS BUILDING BLOCKS FOR ROCKS DEFINITION:
naturally occurring, inorganic solids, consisting of specific chemical elements, and a definite atomic array
CRYSTALLINE STRUCTURE – ‘CRYSTAL’

5. MINERALS MINERALS: TWO CATEGORIES
SILICATES – CONTAIN SILICON & OXYGEN MOLECULES (SiO)
NON-SILICATES (NO SiO)

6. 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)

7. SILICATE MINERALS Make up 90-95% of the Earth’s Crust
Dominant component of most rocks, include:
QUARTZ (SiO2)
FELDSPARS
MICAS

8. ROCKS AGGREGATIONS OF 2 OR MORE MINERALS THREE CATEGORIES
Same or different minerals combine together
THREE CATEGORIES
IGNEOUS
SEDIMENTARY
METAMORPHIC

9. 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

10. IDENTIFICATION OF IGNEOUS ROCKS
IDENTIFICATION PROCESSES:
TEXTURE:
Size, shape and manner of growth of individual crystals
MINERAL COMPOSITION
Based on SiO content

11. 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

12. 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

13. SEDIMENTARY ROCKS
Weathering processes break rock into pieces, sediment, ready for transportation deposition burial lithification into new rocks.

14. 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

15. SEDIMENTARY ENVIRONMENTS
Lakes
Lagoons
Rivers
Ocean bottoms
Estuaries
Salt Flats
Playas
Glacial environments

16. 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.

17. 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

18. Time for a break…

19. 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.

20. 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.

21. 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)

22. DENDROCHRONOLOGY

23. 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

24. VARVE CHRONOLOGY

25. 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.

26. 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