Earth Materials - Exam One

Requirements for a material to be considered a mineral

• Naturally occurring

• Inorganic

• crystalline

• Solid

• Definite but not fixed composition

Meaning and importance of mineral solid solution

Same composition but different minerals

• MgSiO- forsterite and fayalite

• Different heat and pressure scenarios

Igneous rock

interlocking grains, lack of foliation, bubbly or gassy, cross cutting, and dikes

Age of Earth

4.56 Ga (billion years old)

• extraterrestrial samples help to determine age

Compositional layers of earth

Crust, mantle, outer core (liquid), inner core

mechanical layers of earth

lithosphere, asthenosphere, lower mantle (mesospheric mantle), outer core and inner core

Heat transfer mechanisms

• radiation (movement of particles at surface)

• conduction (atomic vibrations from interior to exterior of earth)

• convection (movement of material with different densities from interior to exterior)

• advection (movement of materials at shallow portions)

• no heat transfers - no plate tectonics

Importance of plate tectonics

drives production of melts

Primary Textures

initial rock formation

• crystal growth

• Crystal form (Euhdreal, subhedral, anhedral)

• Grain size (phaneritic, porphyritic, aphanitic)

• zoning

• twinning

Secondary textures

occur after crystallization is complete

• polymorphs

• secondary twinning (tartan)

• Exsolution (mineral unmixing)

• replacement reactions

• deformation (undolse extinction)

magma viscosity and SiO2 content, temperature, and volatile content

more felsic = more viscous (more flow resistant)

inversely proportional to temp and volatile content (less viscous)

Eruptive style

increased viscosity- traps more volatiles that build up pressure → more explosive eruptions

• More felsic = more explosive

Central Vent Landform

melt issues from central vent

• Shield Volcanoes (broad and shallow slope)

• Composite/Stratovolcanoes (steep-sided, explosive and violent)

• Domes (lowly rising intermediate to felsic (viscous) magma)

• Calderas (very explosive eruptions, especially in intermediate to felsic settings)

Non-Central Vent

• Fissure (magma eruption via central fracture or set of Fractures)

• Can drive mass extinction events

Lava flows

generally slow moving

• Columnar Jointing

• pillow lavas (encounter water)

Pyroclastic fall deposits

fragmental volcanic material formed from explosive volcanism

• can be deposited far from the source

Pyroclastic flow deposits

ground hugging debris and extremely fast moving

• lahars - mixture of water and pyroclastic debris to produce fast moving mud flow

Plutons

rise due to lower density and intrude into surrounding country rock

Tabular

sheet like landforms - sill (concordant) or dike (discordant)

Concordant vs discordant

follows country rock structure and discordant does not

Non-tabular

batholith and stock

Possible pluton placement mechanisms

• Lifting of overlying country rock-

• Assimilation/melting of country rock-

• Chunks of country rock sink into
  magma (‘stoping’)

• Ductile wall deformation

• Lateral country rock
  displacement

Thermodynamics

Allows petrologists to qualitatively and quantitatively
assess conditions of rock formation
• Pressure (P), Temperature (T), Composition (X) (of fluids, vapors, or mineral
phases)

Gibbs free energy

G = H – TS

G>0= reactants are most stable

G<0= products more stable

Le Chǎtelier’s Principle

if stress is applied to system it will adjust to return back to equilibrium

Phase rule

F = C – P + 2

for equilibrium

Liquidus

first appearance of solid (going down
temperature) - give you TLC

Solidus

first appearance of liquid (going up temperature) - give you TSC

Eutectic Point

lowest temp conditions of liquid stability, where two liquidi meet (no solid solution)

peritectic point

point on a phase diagram where a reaction takes place between a previously precipitated phase and the liquid to produce a new solid phase

How to H20 impact phase diagram

adding h20 lowers melting point

Hypersolvus

Crystallize above the solvus (contains a single alkali feldspar, may be exsolved)

subsolvus

Crystallize below the solvus
(contains two separate
feldspars)

Major elements

>1.0 wt.% of total rock (e.g., SiO2, Al2O3, FeO, MgO, CaO, Na2O, K2O)

minor elements

0.1 – 1.0 wt% of total rock (e.g., TiO2, MnO, P2O5, and volatile species H2O and CO2)

trace elements

<0.1 wt.% of total rock

Normative Minerology

‘Idealized’ modal mineralogy that can be compared to coarse-grained rocks

• does not include water (anhydrous)

Modal Minerology

minerals that are actually present

• difficult for volcanic rocks because they are so fine grained

Bivariant diagrams

model magma evolution over time based on SiO2

trivariant plots

useful for plotting 3d in 2d - combine variables

• F - Fe0, Fe2O3

• A - K2O, Na2O

• M - MgO