MINERALS AND ROCKS

MINERALS AND ROCKS
IN THE EARTH’S CRUST
Igneous, Sedimentary, Metamorphic Rocks
and Environments
ELEMENTS
• Chemical elements are the fundamental
materials of which all matter is composed.
– From the modern viewpoint:
• a substance that cannot be broken down or
reduced further
PERIODIC TABLE OF ELEMENTS
ELEMENTS
• ALMOST ALL THE MINERALS FOUND IN THE
EARTH ARE FORMED FROM THE BONDING
OF 8 ELEMENTS
• 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)
MINERALS
• BUILDING BLOCKS FOR ROCKS
• DEFINITION:
– NATURALLY OCCURRING,
– INORGANIC SOLIDS,
– CONSISTING OF SPECIFIC CHEMICAL
ELEMENTS, AND
– A DEFINITE ATOMIC ARRAY
• CRYSTALLINE STRUCTURE – ‘CRYSTAL’
Crystalline Mineral Structure
MINERALS
• MINERALS:
• TWO CATEGORIES BASED ON SILICA
CONTENT (SiO – silicon-oxygen molecule)
– SILICATES – CONTAIN SILICON - OXYGEN
MOLECULE (SiO)
– NON-SILICATES (NO SiO)
NON-SILICATE MINERALS
• Non-silicate minerals are very rare
• Make up 5% of Earth’s continental crust
– Considered valuable commercially as building
materials, gemstones, iron ores for steel, ceramics,
and more.
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Native metals: gold, silver, copper
Carbonates: calcite (used in cement)
Oxides: hematite (iron ores)
Sulfides: galena (lead ores)
Sulfates: gypsum (used in plaster, dry wall)
SILICATE MINERALS
• THE MOST ABUNDANT OF ALL MINERALS
– MAKE UP 90-95% OF WEIGHT OF EARTH’S
CRUST
– CONTAIN VARYING AMOUNTS OF SILICA (SiO)
• DOMINANT COMPONENT OF MOST ROCKS:
– IGNEOUS
– SEDIMENTARY
– METAMORPHIC
SILICATE MINERALS
• LISTED BELOW IN DECREASING % OF SILICA ARE
MOST COMMON SILICATE MINERALS
• QUARTZ (SiO2)
(“High” Silica content ~100%)
• FELDSPARS (PLAGIOCLASE - (Na,Ca)(Si,Al)4O8 )
• MICAS (MUSCOVITE -KAl 2(AlSi3O10)(F, OH)2 and
BIOTITE - K (Fe, Mg)3 AlSi3 O10 (F, OH)2 )
• AMPHIBOLES (Hornblende -Ca2(Fe,Mg)5Si8O22(OH2)
• PYROXENES (Augite – {Mg,Fe}SiO 3)
• OLIVINE - (Mg, Fe)2SiO4, (“Low” Silica content ~40%)
FELSIC SILICATE MINERALS
• MINERALS WITH HIGH CONCENTRATION
OF SILICON, OXYGEN, ALUMINIUM AND
POTASSIUM
• FELSIC SILICATES – HIGH % SiO
– QUARTZ (100% SiO 2)
– FELDSPARS (Plagioclase, Orthoclase)
– MUSCOVITE MICA
MAFIC SILICATE MINERALS
• MINERALS WITH HIGH CONCENTRATION
OF MAGNESIUM AND IRON, PLUS
CALCIUM AND SODIUM, AND LOWER
AMOUNTS OF SILICON AND OXYGEN
• MAFIC SILICATES - LESS SiO
– BIOTITE MICA
– AMPHIBOLE (Hornblende)
– PYROXENE (Pyroxene)
ULTRAMAFIC SILICATES
• MINERALS WITH GREATER
CONCENTRATION IN MAGNESIUM AND
IRON. VERY RARE AT EARTH’S SURFACE
• ULTRA MAFIC SILICATES - VERY LOW %
SiO
• VERY RARE AT SURFACE
– OLIVINE
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 FOR
PLUTONIC OR VOLCANIC IGNEOUS
ROCKS:
– TEXTURE:
• Size, shape and manner of growth of individual
crystals
– MINERAL COMPOSITION
• Based on SiO content
– Felsic, Intermediate, Mafic
TEXTURE IDENTIFICATION
• SIZE, SHAPE OF CRYSTALS AND MANNER
OF GROWTH
• APHANITIC TEXTURE:
– FINE-GRAINED – VERY TINY, MINERAL
CRYSTALS VISIBLE ONLY WITH MAGNIFICATION
– INDICATES FAST COOLING AT SURFACE
• PHANERITIC TEXTURE:
– COARSE-GRAINED – LARGE, EASILY-VISIBLE
MINERAL CRYSTALS
– INDICATES SLOW COOLING AT DEPTH
Fine-Grained (Aphanitic) Textures
Coarse-Grained (Phaneritic) Textures
MINERAL COMPOSITION
• CLASSIFIED BY SILICA (SiO) CONTENT
• FELSIC – MORE THAN 85% SILICA
• INTERMEDIATE – 60-85% SILICA
• MAFIC – LESS THAN 60% SILICA
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
IGNEOUS ROCKS
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
CLASTIC SEDIMENTARY ROCKS
• CLASSIFIED ON GRAIN OR PARTICLE
SIZE
• Shales: finest-grained
• Sandstones: medium-grained
• Conglomerates – Breccias: coarse-grained
SHALES
• SHALES: finest-grained – composed of
very small particles (from <0.004-0.063
mm)
– 50% of all sedimentary rocks are Shales
– Consist largely of Clay minerals
– Subcategories: Claystones; Siltstones;
Mudstones
– Economic value: building material; china
and ceramics; spark plug housings
SANDSTONES
• SANDSTONES: medium-grained; particlesize (0.063-2 mm)
• 25% of all sedimentary rocks fall into this
category
• Economic value: glass; natural reservoirs
for oil, gas, and groundwater
CONGLOMERATES - BRECCIAS
• CONGLOMERATES AND BRECCIAS:
• The coarsest of all the detrital sedimentary
rocks
• Composed of particles >2 mm in diameter
– Conglomerate - the particles are rounded
– Breccia - the particles are angular
CHEMICAL SEDIMENTARY
ROCKS
• TWO CATEGORIES:
– INORGANIC CHEMICAL SEDIMENTARY
– ORGANIC CHEMICAL SEDIMENTARY
INORGANIC CHEMICAL
SEDIMENTARY ROCKS
• Formed when dissolved products of
chemical weathering precipitate from
solution
• Most common types:
– Inorganic limestones and cherts: precipitates
directly from seawater and fresh water
– Evaporites: precipitates when ion-rich water
evaporates
– Dolostones: Origin is still in debate
INORGANIC - LIMESTONES
• Limestones - account for 10% - 15% of all
sedimentary rocks formed from Calcite or
Calcium Carbonate (CaCO3).
• Formed as pure carbonate muds accumulate on the sea
floor
• Also formed on land:
– Tufa - a soft spongy inorganic limestone that forms where underground
water surfaces
– Travertine - forms in caves when droplets of carbonate-rich water on the
ceiling, walls and floors precipitate a carbonate rock
ORGANIC LIMESTONES
• Formed with calcite from marine environment: CaCO3
shells and internal/external skeletons of marine animals
• Coquina - “crushed” shell fragments cemented with CaCO3
• Chalk - made from billions of microscopic carbonate-secreting
organisms
• Coral Reefs - Formed from the skeletons of millions of tiny
invertebrate animals who secrete a calcite-rich
material. Live “condo” style while algae acts
as the cement to create the large structures
called “reefs”.
• Organic Chert - formed when silica-secreting microscopic marine
•
organisms die (radiolaria {single-celled animals} and
diatoms {skeletons of singled-celled plants})
• Flint - an example of an Organic Chert
ORGANIC SEDIMENTARY
ROCKS
• Coal - Organic sedimentary rock consisting mainly of plant remains
• Formation:
– Burial of decaying vegetation ;
– Increasing pressure from the overlying layers expels water, CO2 and
other gases;
– Carbon accumulates.
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STAGES:
Peat - formed early in the process, when the original plant structure
can still be distinguished.
Lignite - a more hardened form of Peat
Bituminous - more pressure and more heat produce this moderately
hard coal.
Anthracite - the hardest coal - formed from metamorphic processes
under extreme heat and pressure - Hard - Shiny - the most
desired as an energy resource.
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
• Ion-rich fluids circulating in and around rocks
also influences metamorphism
METAMORPHIC PROCESSES
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HEAT: Temperatures needed to
metamorphose rock (2000 C or
4000 F) reached near 10 km (6
miles) beneath the surface.
PRESSURE: Requires pressure
> 1 bar or 1000 mb, which is
generally found ~ 3 km (2 miles)
beneath the Earth’s surface
FLUIDS: Water is the usual
fluid and comes from various
sources
TEMPERATURE/PRESSURE
– For every 3 kilometers depth in
the Earth, pressure increases by
about 1 kb.
– Average temperature gradient in
the Earth increases 30° C per km
CHANGES IN METAMORPHIC
ROCKS
• Metamorphic processes cause many
changes in rocks
– increased density
– growth of larger crystals
– reorientation of the mineral grains into layers
or banded texture
• FOLIATION
– transformation of low-temperature minerals
into high-temperature minerals
CLASSIFYING METAMORPHIC
ROCKS
• TEXTURE: the size, shape and
distribution of particles in a rock
– texture is determined by grade of
metamorphism
• Low grade: (less than 6000C and 4 kilobars pressure)
• Intermediate grade: occurs at a variety of temperatures
and pressures.
• High grade: (greater than 6000C and 4 kilobars pressure)
FOLIATED TEXTURES
• Foliated texture: more pressure and mineral
grains realign themselves and grow into larger
crystals
• Three types of foliated texture:
– Rock or Slaty Texture
– Schistosity
– Gneissic Texture
ROCK – SLATY TEXTURE SLATE
• Shale metamorphosed to Slate:
– clay minerals (stable at surface temperatures
and pressures) become unstable and
recrystallize into mica crystals
– Slate is formed under Low-Grade
Metamorphism
SCHISTOCITY - SCHIST
• More extreme pressures and temperatures: mica
crystals grow even larger - ~ 1 cm in diameter.
– rock has “scaly” appearance - schistosity,
– referred to as a Schist.
• Schists formed under Intermediate-Grade
Metamorphism
• Schists named for the mineral constituents in the parent
rock:
– mica schist
– talc schist
– garnet schist
GNEISSIC TEXTURE - GNEISS
• Light and dark silicate minerals separate and realign themselves into bands
• Rocks with this texture are called Gneiss
• Gneiss forms from High Grade Metamorphism
• Typical ‘parent’ rocks for Gneiss
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granite
diorite
gabbro
shale.
NON-FOLIATED TEXTURES
• Rocks with only one mineral
metamorphose without a visibly foliated
texture
• Limestone metamorphoses into Marble
as the interlocking calcite crystals grow
larger
• Quartz Sandstone metamorphoses into
Quartzite
METAMORPHIC ENVIRONMENTS
• CONTACT METAMORPHISM
– Metamorphism of a rock touched by the intense heat of migrating
magma.
• REGIONAL METAMORPHISM
– Burial metamorphism - occurs when rocks are overlain by more than 6
miles of rock or sediment
– Dynamothermal metamorphism - occurs when rocks are caught
between two convergent plates during mountain building
• OTHER METAMORPHIC ENVIRONMENTS
– Hydrothermal metamorphism - chemical alteration of preexisting
rocks by hot seawater near seafloor spreading or subduction zones
– Fault metamorphism - occurs as rocks grinding past one another
create a form of directed pressure, as well as considerable frictional
heat
– Shock metamorphism - occurs when a meterorite strikes the Earth
surface, resulting in tremendous pressures and temperatures at the
impact sites. The “shocked” minerals do not fracture, but rather
recrystallize
Contact and Regional
Metamorphism
Rock Cycle