Transcript MINERALS AND ROCKS - Los Angeles Mission College

MINERALS AND ROCKS
IN THE EARTH’S CRUST
Igneous, Sedimentary, Metamorphic
Rocks and Environments
MINERALS AND ROCKS COME
FROM 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
MAKING MINERALS FROM
ELEMENTS
• ALMOST ALL THE MINERALS FOUND IN THE EARTH ARE
FORMED FROM THE BONDING OF EIGHT (8) ELEMENTS
– OXYGEN (O)
MOST ABUNDANT
– SILICON (Si)
– ALUMINIUM (Al)
– IRON (Fe)
– CALCIUM (Ca)
– POTASSIUM (K)
– SODIUM (Na)
LEAST ABUNDANT
– MAGNESIUM (Mg)
WHAT ARE MINERALS?
• BUILDING BLOCKS FOR ROCKS
• DEFINITION:
– NATURALLY OCCURRING,
– INORGANIC SOLIDS,
– CONSISTING OF SPECIFIC CHEMICAL
ELEMENTS, AND
– A DEFINITE ATOMIC ARRAY
• CRYSTALLINE STRUCTURE – ‘CRYSTAL’
• ‘CRYSTAL’ AND ‘MINERAL’
INTERCHANGEABLE TERMS
MINERALS
Minerals divided into two main groups
based on Silica content
Silica (SiO) compound of molecularly bonded
silicon (Si) and oxygen (O) molecules (SiO,
SiO2, SiO4, SiO6 etc.)
GROUP 1: SILICATES – CONTAIN
SILICA
GROUP 2: NON-SILICATES
(CONTAIN NO SILICA)
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.
• Native metals: gold, silver, copper, platinum
• Native elements: diamonds, corundum: Ruby
(red) or Sapphire (blue)
• Carbonates: calcite (used in cement)
• Oxides: hematite (iron ores)
• Sulfides: galena (lead ores)
• Sulfates: gypsum (used in plaster, dry wall)
• Halides: halite (table salt)
SILICATE MINERALS
• THE MOST ABUNDANT OF ALL MINERALS
– MAKE UP APPROXIMATELY 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 -KAl2(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) SiO3)
– OLIVINE - (Mg, Fe)2SiO4,
(“Low” Silica content ~40%)
SILICATE MINERALS
• SILICATE MINERALS ARE BROKEN
INTO THREE MAIN GROUPS
ACCORDING TO % SILICA
– FELSIC
– MAFIC
– ULTRAMAFIC
High percent
Low percent
FELSIC SILICATE MINERALS
• FELSIC SILICATE MINERALS HAVE A
HIGH CONCENTRATION OF SILICON,
OXYGEN, ALUMINIUM AND POTASSIUM
• FELSIC SILICATES – HIGH % SiO (75100%)
– QUARTZ (100% SiO2)
– FELDSPARS (Plagioclase, Orthoclase)
– MUSCOVITE MICA
QUARTZ
FELDSPAR
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 (50-60%)
– BIOTITE MICA
– AMPHIBOLE (Hornblende)
– PYROXENE (Augite)
BIOTITE MICA
PYROXENE (AUGITE)
AMPHIBOLE
(HORNBLENDE)
ULTRAMAFIC SILICATES
• MINERALS WITH GREATER
CONCENTRATION IN MAGNESIUM AND
IRON. VERY RARE AT EARTH’S SURFACE
• ULTRA MAFIC SILICATES - VERY LOW %
SiO (less than 50%)
• VERY RARE AT SURFACE
– OLIVINE (FORSTERITE, FAYALITE)
WHAT ARE ROCKS?
• AGGREGATIONS OF 2 OR MORE
MINERALS
– Same or different minerals combine
together
• THREE CATEGORIES
– IGNEOUS
– SEDIMENTARY
– METAMORPHIC
IGNEOUS ROCKS
• Ignis: Latin for “Fire”
• FORMED FROM COOLED, SOLIDIFIED
MOLTEN MATERIAL AT, NEAR, OR DEEP
BELOW, THE SURFACE
• TYPES:
– PLUTONIC (INTRUSIVE) –IGNEOUS ROCKS
COOLED AND SOLIDIFIED BELOW SURFACE AT
GREAT DEPTHS
– VOLCANIC (EXTRUSIVE) – IGNEOUS ROCKS
COOLED AND SOLIDIFIED AT OR NEAR THE
SURFACE THROUGH VOLCANIC ERUPTIONS
IDENTIFICATION OF IGNEOUS
ROCKS
• TWO 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
– (high Silica
low Silica)
TEXTURE IDENTIFICATION
• SIZE, SHAPE OF CRYSTALS AND MANNER OF
GROWTH
• FINE GRAINED TEXTURE:
– VERY TINY, MINERAL CRYSTALS VISIBLE
ONLY WITH MAGNIFICATION
– INDICATES FAST COOLING AT SURFACE –
CRYSTALS SOLIDIFIED QUICKLY WITH NO
TIME TO ‘GROW’
• COARSE-GRAINED TEXTURE:
– LARGE, EASILY-VISIBLE MINERAL CRYSTALS
– INDICATES SLOW COOLING AT DEPTH –
CRYSTALS SOLIDIFIED SLOWLY WITH LOTS
OF TIME TO ‘GROW’
TEXTURE IDENTIFICATION
Fine-Grained Textures
Coarse-Grained Textures
MINERAL COMPOSITION
• CLASSIFIED BY SILICA (SiO)
CONTENT
• FELSIC – MORE THAN 85% SILICA
• INTERMEDIATE – 60-85% SILICA
• MAFIC – LESS THAN 60% SILICA
MINERAL COMPOSITION OF COMMON
IGNEOUS ROCKS
• FELSIC IGNEOUS ROCKS (>85% SiO)
– GRANITE:
• PLUTONIC-INTRUSIVE; PHANERITIC TEXTURE; FELSIC MINERAL COMPOSITION
– RHYOLITE:
•
VOLCANIC-EXTRUSIVE; APHANITIC TEXTURE; FELSIC MINERAL COMPOSITION
• INTERMEDIATE IGNEOUS ROCKS (60-85% SiO)
– DIORITE:
• PLUTONIC-INTRUSIVE; PHANERITIC TEXTURE; INTERMEDIATE MINERAL
COMPOSITION
– ANDESITE:
• VOLCANIC-EXTRUSIVE; APHANITIC TEXTURE; INTERMEDIATE MINERAL
COMPOSITION
• MAFIC IGNEOUS ROCKS (<60% SiO)
– GABBRO: PLUTONIC-
• INTRUSIVE; PHANERITIC TEXTURE; MAFIC MINERAL COMPOSITION
– BASALT:
• VOLCANIC-EXTRUSIVE; APHANITIC TEXTURE; MAFIC MINERAL COMPOSITION
FELSIC IGNEOUS ROCKS
RHYOLITE
EXTRUSIVE
INTRUSIVE
GRANITE
INTERMEDIATE IGNEOUS
ROCKS
ANDESITE
DIORITE INTRUSIVE
EXTRUSIVE
MAFIC IGNEOUS ROCKS
GABBRO INTRUSIVE
BASALT EXTRUSIVE
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
VOLCANIC GLASS
OBSIDIAN
PUMICE
PYROCLASTIC IGNEOUS ROCKS
WELDED TUFF
SEDIMENTARY ROCKS
• WEATHERING PROCESSES BREAK
ROCK INTO PIECES, SEDIMENT.
• READY FOR SEDIMENTATION
PROCESSES:
– TRANSPORTATION
DEPOSITION
BURIAL AND LITHIFICATION INTO
NEW ROCKS.
SEDIMENTARY PROCESSES
• LITHIFICATION:
• As sediment is buried several kilometers beneath the surface,
heated from below, pressure from overlying layers, heat, 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.
CLASSIFYING SEDIMENTARY
ROCKS
• THREE SOURCES FOR SEDIMENTARY ROCKS
• Detrital (or clastic) sediment is composed of
transported solid fragments (or detritus) of preexisting 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/DETRITAL
SEDIMENTARY ROCKS
• CLASSIFIED ON GRAIN OR PARTICLE
SIZE
• Shales: finest-grained
• Sandstones: medium-grained
• Conglomerates – Breccias: coarsegrained
SHALES : CLASTIC
SEDIMENTARY
• SHALES: finest-grained clastic sedimentary rocks
– composed of very small particles (from <0.0040.063 mm)
– 50% of all sedimentary rocks are Shales
– Consist largely of Clay minerals (weathered
granite in many cases)
– Subcategories: Claystones; Siltstones;
Mudstones
– Economic value: building material; china and
ceramics; spark plug housings
SHALES
Burgess
Shale in
Canada
Limestone on black shale
MUDSTONES, SILTSTONES
Identified by decreasing amounts of
sand and increasing amounts of clay
SANDSTONES
• SANDSTONES: medium-grained
clastic sedimentary rocks; particlesize (0.063-2 mm)
• 25% of all sedimentary rocks fall into
this category
• Economic value: glass; natural
reservoirs for oil, gas, and
groundwater
SANDSTONES
CONGLOMERATES - BRECCIAS
• CONGLOMERATES AND
BRECCIAS:
• The coarsest of all the clastic
sedimentary rocks
• Composed of particles >2 mm in
diameter
– Conglomerate - the particles are
rounded
– Breccia - the particles are angular
CONGLOMERATES
BRECCIAS
CHEMICAL SEDIMENTARY
ROCKS
• TWO CATEGORIES:
– INORGANIC CHEMICAL SEDIMENTARY
– ORGANIC CHEMICAL SEDIMENTARY
INORGANIC CHEMICAL
SEDIMENTARY ROCKS
• Formed when dissolved products of
chemical weathering precipitate (‘form out
of’) 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: stalactites and stalagmites
LIMESTONES
TRAVERTINE
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 carbonatesecreting 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 Inorganic Chert
COQUINA, CHALK AND
FOSSILIFEROUS LIMESTONES
COQUINA
FOSSILIFEROUS
LIMESTONE
CHALK
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.
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.
COAL
PEAT
LIGNITE
ANTHRACITE
BITUMINOUS
SEDIMENTARY ENVIRONMENTS
•
•
•
•
•
•
•
•
Lakes
Lagoons
Rivers
Ocean bottoms
Estuaries
Salt Flats
Playas
Glacial environments
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
• HEAT:
– (2000 C or 4000 F) reached
near 10 km (6 miles)
beneath the surface.
• PRESSURE:
– > 2 bar or 2000 mb, which
is generally found ~ 6 km
(4 miles) beneath the
Earth’s surface
• FLUIDS: Chemicallyactive 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
– FOLIATION : reorientation of the
mineral grains into layers or banded
texture
– 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
SLATE
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
SCHIST
Mica schist
Ruby schist
GNEISSIC TEXTURE - GNEISS
• Light and dark silicate minerals separate
and re-align themselves into bands
• Rocks with this texture are called Gneiss
• Gneiss forms from High Grade
Metamorphism
• Typical ‘parent’ rocks for Gneiss
–
–
–
–
granite
diorite
gabbro
shale
GNEISS
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
MARBLE AND QUARTZITE
MARBLE
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
Regional
Metamorphism
Contact Metamorphism
ROCK FORMING PROCESSES
THE ROCK CYCLE