MINERALS AND ROCKS MINERALS AND ROCKS IN THE EARTHIN THE EARTH’’S CRUSTS CRUSTIgneous, Sedimentary, Metamorphic Rocks Igneous, Sedimentary, Metamorphic Rocks

and Environmentsand Environments

ELEMENTSELEMENTS

• 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

ELEMENTSELEMENTS• ALMOST ALL THE MINERALS FOUND IN THE

EARTH ARE FORMED FROM THE BONDING OF 8 ELEMENTS

• LISTED IN ORDER OF ABUNDANCE– OXYGEN (O)– SILICON (Si)– ALUMINIUM (Al)– IRON (Fe)– CALCIUM (Ca)– POTASSIUM (K)– SODIUM (Na)– MAGNESIUM (Mg)

MINERALSMINERALS

• BUILDING BLOCKS FOR ROCKS• DEFINITION:

– NATURALLY OCCURRING, – INORGANIC SOLIDS, – CONSISTING OF SPECIFIC CHEMICAL

ELEMENTS, AND – A DEFINITE ATOMIC ARRAY

• CRYSTALLINE STRUCTURE – ‘CRYSTAL’

Crystalline Mineral StructureCrystalline Mineral Structure

MINERALSMINERALS

• MINERALS: • TWO CATEGORIES BASED ON SILICA

CONTENT (SiO – silicon-oxygen molecule)– SILICATES – CONTAIN SILICON - OXYGEN

MOLECULE (SiO)– NON-SILICATES (NO SiO)

NONNON--SILICATE MINERALSSILICATE 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• Carbonates: calcite (used in cement)• Oxides: hematite (iron ores)• Sulfides: galena (lead ores)• Sulfates: gypsum (used in plaster, dry wall)

SILICATE MINERALSSILICATE 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 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%)

FELSIC SILICATE MINERALS FELSIC SILICATE MINERALS

• MINERALS WITH HIGH CONCENTRATION OF SILICON, OXYGEN, ALUMINIUM AND POTASSIUM

• FELSIC SILICATES – HIGH % SiO– QUARTZ (100% SiO2)– FELDSPARS (Plagioclase, Orthoclase)– 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– BIOTITE MICA– AMPHIBOLE (Hornblende)– PYROXENE (Pyroxene)

ULTRAMAFIC SILICATESULTRAMAFIC 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

ROCKSROCKS

• AGGREGATIONS OF 2 OR MORE MINERALS– Same or different minerals combine together

• THREE CATEGORIES– IGNEOUS– SEDIMENTARY– METAMORPHIC

IGNEOUS ROCKSIGNEOUS 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 IDENTIFICATION OF IGNEOUS ROCKSROCKS

• 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 IDENTIFICATIONTEXTURE 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 COMPOSITIONMINERAL COMPOSITION

• CLASSIFIED BY SILICA (SiO) CONTENT

• FELSIC – MORE THAN 85% SILICA

• INTERMEDIATE – 60-85% SILICA

• MAFIC – LESS THAN 60% SILICA

COMMON IGNEOUS ROCKSCOMMON 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 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

SEDIMENTARY ROCKSSEDIMENTARY ROCKS

• WEATHERING PROCESSES BREAK ROCK INTO PIECES, SEDIMENT, READY FOR TRANSPORTATION DEPOSITION BURIAL LITHIFICATION INTO NEW ROCKS.

CLASSIFYING SEDIMENTARY CLASSIFYING SEDIMENTARY ROCKSROCKS

• 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 ROCKSCLASTIC SEDIMENTARY ROCKS• CLASSIFIED ON GRAIN OR PARTICLE

SIZE• Shales: finest-grained• Sandstones: medium-grained• Conglomerates – Breccias: coarse-grained

SHALESSHALES

• 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

SANDSTONESSANDSTONES• SANDSTONES: medium-grained; 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

CONGLOMERATES CONGLOMERATES -- BRECCIASBRECCIAS

• 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 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 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 INORGANIC -- LIMESTONESLIMESTONES

• 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 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 Organic Chert

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.

SEDIMENTARY ENVIRONMENTSSEDIMENTARY ENVIRONMENTS

• Lakes• Lagoons• Rivers• Ocean bottoms

• Estuaries• Salt Flats• Playas• Glacial environments

SEDIMENTARY PROCESSESSEDIMENTARY PROCESSES

• LITHIFICATION:• As sediment is buried several kilometers beneath the surface, heated from

below, pressure from overlying layers and chemically-active waterconverts 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 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: 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 CHANGES IN METAMORPHIC ROCKSROCKS

• 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 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 ROCK –– SLATY TEXTURE 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

SCHISTOCITY SCHISTOCITY -- SCHISTSCHIST• 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 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.

NONNON--FOLIATED TEXTURESFOLIATED TEXTURES

• Rocks with only one mineral metamorphose without a visibly foliated texture

• Limestone metamorphoses into Marbleas the interlocking calcite crystals grow larger

• Quartz Sandstone metamorphoses into 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

Rock CycleRock Cycle