EESA06 Topic 5: Earth Materials

what is a rock?

• naturally formed, consolidated material

• composed of grains of 1+ minerals

what is a mineral?

• naturally occuring, inorganic crystalline solid

• has a specific chemical composition

• building blocks of rocks

what are some common minerals in Earth’s crust? which is the most important and why?

• quartz

• feldspar

  • most important because it is common in both continental and oceanic crust

• biotite

what are 2 characteristics do all minerals have unique to them?

• prescribed composition

  • i.e., a chemical formula

• structural arrangement

  • i.e., a crystal lattice

describe the crystal lattice of a mineral

a ridigid structure describing how elements are arranged in a mineral

do chemical formulas have range?

• yes

• some elements can be substituted for others due to similarities

define rockhounding

the hobby of searching for and collecting rocks and minerals

how can you differentiate minerals?

• streak

• colour

• shape

• cleavage

• harness

• lustre

is using colour a reliable way to identify minerals? describe.

• no - it’s the least accurate, despite being the most noticable

• any little impurity can change the colour, despite

  • same chemical structure

  • similar physical characteristics

describe the streak of a mineral

• the colour of the fine powder produced by rubbing a mineral on a streak plate

• e.g., hematite - red/brown (image)

define crystallography

the study of crystal shapes

what can the crystal shape be reflective of?

if grown in an uninhibited manner, shape can reflect a mineral’s crystal lattice

define mineral cleavage

• the shape of mineral when broken

• tendency for minerals to break (or cleave) along regular plains where the crystal structure is weak

describe the characteristics of mica

• composed of biotite and muscovite

• e.g. of a mineral with good cleavage

• used in make-up, electronics, etc.

define lustre

the way light is reflected in a mineral

what are the different descriptor words for lustre?

• submetallic

• adamantine

• pearly

• silky

• greasy

• dull

• vitreous

• earthy

• resinous

• metallic

define vitreous lustre and give an example of a mineral with this lustre

• reflects white light like glass

• e.g., quartz

define hardness

the scratchability of a mineral

what scales can measure mineral hardness? how do they differ?

• Mohs hardness scale

• Vickers hardness test

difference → Vickers is more objective than Mohs

how might you use soft minerals vs. hard minerals?

• soft → lubricants

• hard → drilling (e.g., industrial diamonds)

what are the most important group of minerals? why?

• silicate minerals - i.e., those containing silicon and oxygen (SiO₃)

• they make up 90% of all minerals

where are non-silicate minerals most common?

the continental crust (i.e., not oceanic)

what are the most common non-silicate minerals?

• carbonates

• evaporites

• metallic minerals

describe and give examples of carbonates

• often products of organism decay (e.g., shelled animals)

  • CO₃ released from their skeletons

• often found in limestone

• e.g., calcite, dolomite

describe and give examples of evaprites

• formed from fluid evaporation (e.g., salt water)

• e.g., halite

describe and give examples of ores (i.e., metallic minerals)

• main components are metals, which are joined with sulphur or oxygen

• e.g., galena (lead), sphalerite (zinc)

what is the importance of ores?

• they’re the foundation of mineral resource industry

• i.e., sustains our societies dependance on consuming large volumes of metals

what are the stages of the Life Cycle of a Mine (mineral resource development cycle)?

• exploration

• discovery

• development

• production

• reclamation

what is gangue?

• unwanted “stuff” in ore

• i.e., by-product of mining for metal

why is gangue an environmental issue?

• there is a large quantity

• lots of surface area + water interaction → dangerous by-product

• i.e., it is important to know what to do with it after mining

what is the role of prospectors in the mineral resource development cycle?

the exploration for mineral resources

describe placer deposits and why panning is beneficial to find them?

• natural accumulation of minerals that have been eroded from their original source

• they’re concentrated at the surface, making them easily accessible by panning

how can geophysics help during the prospecting stage of the mineral resource development cycle?

• magnetometry

  • e.g., is there a magnetic anomoly

• gravimetry

  • e.g., is gravity too high?

• seismic

  • i.e., help generate a piture of underground

• electrical conductivity

  • different minerals = different electrical conductivity → send electrical current

when might you use geochemical anomolies versus panning?

• geochemical anomolies can be best if panning is too disruptive

• e.g., to ecosystems in streams

what is the Canadian Shield and how discovered?

what

• where many Canadian mineral deposits are

• old rock + different rock types in contact + hydrothermal circulation → mineral deposits

when

• magnetometry

• (they were covered by sedimentary rocks)

what must developers do to get a mine built?

• raise capital

• develop ore body models

• environmental assessments and reclamation plans

• economic viability feasibilty

• regulations

• construction

• production

What process is responsible for the concentration of metals in old rocks?

• Hydrothermal alteration

• hot fluids move through rocks, carrying and depositing minerals

What are two geological features often associated with hydrothermal alteration?

• faults

• magmatic bodies.

What is an example of hydrothermal mineral deposition found on the ocean floor?

• Black smokers

• i.e., hydrothermal vents that emit mineral-rich fluids.

How do metallic mineral veins form?

Hot fluids move through rock fractures, carrying minerals that crystallize and form veins.

What type of mineral deposit is shown in the second image (gold veins in rock)?

• hydrothermal vein deposit

• e.g., minerals like gold are deposited by circulating hot fluids

is “green energy” an entirely “green” process?

• no

• many minerals — therefore a lot of mining — is needed to make “green energy"

describe the elements of the rock cycle

key notes:

• weathering = rocks broken down into small particles

• transportation = particles move

• deposition = particles rest in new place

what processes are metamorphic rocks the result of?

• conditions influencing sedimentary and igneous rock stability

• e.g., pressure + heat → metamorphasis

how does magma differentiate?

• different minerals crystalize at different temperatures

  • e.g., mafic at higher temperatures than felsic

• differentiation can occur when the solid and liquid separate

describe pegmatities and how they arise

what

• igneous rocks

• tend to be last remnants of a cooling magma chamber

• very silica-rich

• very large crystals

how

• extreme magma differentiation

what are pegmatites enriched in?

• lithium

• rare earth elements

• industrial minerals (e.g., mica)

what are incompatable elements?

elements that try to crystalize out of a structure

what are some uses of igneous rocks?

• tell tectonic situations

  • different types at different ancient plate boundaries

• building

  • building facades

  • countertops

  • flooring

  • landscaping

  • monuments

why are igneous rocks useful for building?

they are

• hard

• homogenous

• often locally abundant

what are sedimentary rocks the result of?

• the breakdown of surface rocks

• sediments interacting with the surface of Earth

describe weathering

breaking rock forms into small pieces/particles

describe transportation

• moving particles

• requires an agenet to move them (e.g., wind, water, gravity)

describe deposition

leying particles down

describe lithification

• grains/particles get compacted

• pores close as a result of some force

• fuild precipitates out

what can sedimentary rocks tell us about Earth history?

• what was the Earth like in the past?

• how has climate changes?

• how has life changed?

differentiate what igneous and sedimentary rocks tell us about the Earth

• igneous → plate tectonics

• sedimentary → activity on the surface

list 2 types of weathering

• mechanical

• chemical

what are clastic rocks? list some types.

• sedimentary rocks made of fragments, or clasts, of pre-existing rocks

• e.g.,

  • mudstone

  • sandstone

  • conglomerate

  • breccia

what do textural analyses of rocks tell you?

how grains are transported

describe sedimentary structures

• physical features of sedimentary rocks, such as bedding, ripple marks, and mud cracks

• left behind by transportation of sediment

• evidence of surface processes

what are ichnoFossils?

• fossils recording biological movement

• i.e., biological modes of transportation

describe chemical weathering

• breakdown of minerals by water

• can be dissolved into ions or altered into a new mineral

• dissolved ions can be precipitated into other rocks

why is the ocean salty?

• it’s the end point for water that dissolves minerals

• i.e., high mineral content → salty

differentiate between biochemical rocks and chemical rocks

• biochemical → sedimentary rocks that form from the remains of living organisms

  • e.g., limestone

• chemical rocks → rocks formed from evaporation of water and the precipitation of ions over time

  • e.g., evaporite

what are evaporites and what mineral are they high in?

• rocks produced by seawater evaporation

• high in lithium

what are bioclastic carbonate rocks?

• clastic and biochemical rocks

• e.g., coral reef that gets weathered and moved

what is stratigraphy?

using “layers” to reconstruct a sequence of events

what resources are held in sedimentary rock?

• water

• hydrocarbons (oil, gas)

• coal

• metals (ore bodies)

• placer deposits (gold, diamond, etc.)

• aggregate, cement, building stone, etc.

• industrial minerals

what are metamorphic rocks the result of?

• alteration without melting

• mineral change when rocks undergo changes in heat and pressure

what might metamorphic rocks be used for?

• reconstructing paleotectonics

• mineral deposits

• building stones

what are the 3 types of metamorphism?

• contact metamorphism

• regional metamorphism

• hydrothermal metamorphism

describe contact metamorphism

• parent rock is altered because it’s sitting next to something very hot (e.g., magma chamber)

• i.e. heat-induced metamorphism

describe regional metamorphism

• rock subjected to heat and pressure

  • e.g., under a mountain belt

• cover a large area

• most common in Ontario

describe hydrothermal metamorphism

• hot water removes or adds elements

• e.e., basalt → serpentinite

what is a gneiss?

• a high grade metamorphic rock

• formed deep within the crust

what does shearing a gneiss produce?

mylonite

what does melting a gneiss produce?

• migmatite

• i.e., when gneiss wants to turn into magma