MINERALS AND ROCKS IN MINERALS AND ROCKS IN THE EARTH’S CRUST THE EARTH’S CRUST Igneous, Sedimentary, Metamorphic Igneous, Sedimentary, Metamorphic Rocks and Environments Rocks and Environments
Feb 25, 2016
MINERALS AND ROCKS IN MINERALS AND ROCKS IN THE EARTH’S CRUSTTHE EARTH’S CRUST
Igneous, Sedimentary, Metamorphic Igneous, Sedimentary, Metamorphic Rocks and EnvironmentsRocks and Environments
MINERALS AND ROCKS COME MINERALS AND ROCKS COME FROM ELEMENTSFROM 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 ELEMENTSPERIODIC TABLE OF ELEMENTS
MAKING MINERALS FROM MAKING MINERALS FROM ELEMENTSELEMENTS
• ALMOST ALL THE MINERALS FOUND IN THE EARTH ARE FORMED FROM THE BONDING OF EIGHT (8) ELEMENTS– OXYGEN (O)– SILICON (Si)– ALUMINIUM (Al)– IRON (Fe)– CALCIUM (Ca)– POTASSIUM (K)– SODIUM (Na)– MAGNESIUM (Mg)
MOST ABUNDANT
LEAST ABUNDANT
WHAT ARE MINERALS?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
MINERALSMINERALSMinerals divided into two main groups
based on Silica contentSilica (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 MINERALSNON-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 MINERALSSILICATE 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 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 MINERALSSILICATE MINERALS
• SILICATE MINERALS ARE BROKEN INTO THREE MAIN GROUPS ACCORDING TO % SILICA– FELSIC High percent
– MAFIC– ULTRAMAFIC Low percent
FELSIC SILICATE MINERALS FELSIC SILICATE MINERALS
• FELSIC SILICATE MINERALS HAVE A HIGH CONCENTRATION OF SILICON, OXYGEN, ALUMINIUM AND POTASSIUM
• FELSIC SILICATES – HIGH % SiO (75-100%)– QUARTZ (100% SiO2)– FELDSPARS (Plagioclase, Orthoclase)– MUSCOVITE MICA
FELDSPARQUARTZ
MUSCOVITE MICA
MAFIC SILICATE MINERALSMAFIC 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
AMPHIBOLE (HORNBLENDE)
PYROXENE (AUGITE)
ULTRAMAFIC SILICATESULTRAMAFIC 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?WHAT ARE ROCKS?
• AGGREGATIONS OF 2 OR MORE MINERALS– Same or different minerals combine
together• THREE CATEGORIES
– IGNEOUS– SEDIMENTARY– METAMORPHIC
IGNEOUS ROCKSIGNEOUS 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 IDENTIFICATION OF IGNEOUS ROCKSROCKS
• 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 IDENTIFICATIONTEXTURE 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’
Fine-Grained Textures Coarse-Grained Textures
TEXTURE IDENTIFICATIONTEXTURE IDENTIFICATION
MINERAL COMPOSITIONMINERAL COMPOSITION
• CLASSIFIED BY SILICA (SiO) CONTENT
• FELSIC – MORE THAN 85% SILICA
• INTERMEDIATE – 60-85% SILICA
• MAFIC – LESS THAN 60% SILICA
MINERAL COMPOSITION OF COMMON MINERAL COMPOSITION OF COMMON IGNEOUS ROCKSIGNEOUS 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 ROCKSFELSIC IGNEOUS ROCKSRHYOLITE
GRANITE
EXTRUSIVE
INTRUSIVE
INTERMEDIATE IGNEOUS INTERMEDIATE IGNEOUS ROCKSROCKS
DIORITE
ANDESITE
INTRUSIVE
EXTRUSIVE
MAFIC IGNEOUS ROCKSMAFIC IGNEOUS ROCKS
BASALT
GABBRO
EXTRUSIVE
INTRUSIVE
IGNEOUS ROCKSIGNEOUS ROCKS
OTHER IGNEOUS ROCKSOTHER 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 GLASSVOLCANIC GLASS
OBSIDIAN
PUMICE
PYROCLASTIC IGNEOUS ROCKSPYROCLASTIC IGNEOUS ROCKS
WELDED TUFF
SEDIMENTARY ROCKSSEDIMENTARY ROCKS
• WEATHERING PROCESSES BREAK ROCK INTO PIECES, SEDIMENT.
• READY FOR SEDIMENTATION PROCESSES:– TRANSPORTATION DEPOSITION
BURIAL AND LITHIFICATION INTO NEW ROCKS.
SEDIMENTARY PROCESSESSEDIMENTARY 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 CLASSIFYING SEDIMENTARY ROCKSROCKS
• THREE SOURCES FOR SEDIMENTARY ROCKS
• 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/DETRITAL CLASTIC/DETRITAL SEDIMENTARY ROCKSSEDIMENTARY ROCKS
• CLASSIFIED ON GRAIN OR PARTICLE SIZE
• Shales: finest-grained• Sandstones: medium-grained• Conglomerates – Breccias: coarse-
grained
SHALES : CLASTIC SHALES : CLASTIC SEDIMENTARYSEDIMENTARY
• SHALES: finest-grained clastic sedimentary rocks – composed of very small particles (from <0.004-0.063 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
SHALESSHALES
Limestone on black shale
Burgess Shale in Canada
MUDSTONES, SILTSTONESMUDSTONES, SILTSTONESIdentified by decreasing amounts of sand and increasing amounts of clay
SANDSTONESSANDSTONES• SANDSTONES: medium-grained
clastic sedimentary rocks; particle-size (0.063-2 mm)
• 25% of all sedimentary rocks fall into this category
• Economic value: glass; natural reservoirs for oil, gas, and groundwater
SANDSTONESSANDSTONES
CONGLOMERATES - BRECCIASCONGLOMERATES - 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
CONGLOMERATESCONGLOMERATES
BRECCIASBRECCIAS
CHEMICAL SEDIMENTARY CHEMICAL SEDIMENTARY ROCKSROCKS
• TWO CATEGORIES:
– INORGANIC CHEMICAL SEDIMENTARY
– ORGANIC CHEMICAL SEDIMENTARY
INORGANIC CHEMICAL INORGANIC CHEMICAL SEDIMENTARY ROCKSSEDIMENTARY 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 - LIMESTONESINORGANIC - 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
LIMESTONESLIMESTONESTRAVERTINE
ORGANIC LIMESTONESORGANIC 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 Inorganic Chert
COQUINA, CHALK AND COQUINA, CHALK AND FOSSILIFEROUS LIMESTONESFOSSILIFEROUS LIMESTONES
COQUINA
CHALK
FOSSILIFEROUS LIMESTONE
ORGANIC SEDIMENTARY ORGANIC SEDIMENTARY ROCKSROCKS
• 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.
COALCOALPEAT LIGNITE
BITUMINOUSANTHRACITE
SEDIMENTARY ENVIRONMENTSSEDIMENTARY ENVIRONMENTS
• Lakes• Lagoons• Rivers• Ocean bottoms
• Estuaries• Salt Flats• Playas• Glacial environments
METAMORPHIC ROCKSMETAMORPHIC 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 PROCESSESMETAMORPHIC 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: Chemically-active 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 CHANGES IN METAMORPHIC ROCKSROCKS
• 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 CLASSIFYING METAMORPHIC ROCKSROCKS
• 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 TEXTURESFOLIATED 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 - ROCK – SLATY TEXTURE - SLATESLATE
• 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
SLATESLATE
SCHISTOCITY - SCHISTSCHISTOCITY - 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
SCHISTSCHIST
Ruby schist
Mica schist
GNEISSIC TEXTURE - GNEISSIC TEXTURE - GNEISSGNEISS
• 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
GNEISSGNEISS
NON-FOLIATED TEXTURESNON-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 QUARTZITEMARBLE AND QUARTZITE
MARBLE
QUARTZITE
METAMORPHIC ENVIRONMENTSMETAMORPHIC 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 Contact and Regional MetamorphismMetamorphism
Contact Metamorphism
Regional Metamorphism
ROCK FORMING ROCK FORMING PROCESSESPROCESSES
THE ROCK CYCLE