ERTH1005 WK1-5

What is the problem with calling it ‘critical minerals"‘?

1. different definitions of what it considered ‘critical’ for different countries with their different purposes, like silica in aus

2. not all commodities are minerals like the phrase suggests, like nickel, which is an element

critical mineral definitions

Critical minerals” is a misnomer. The term critical
minerals actually refer to commodities (actually
elements, not minerals) extracted from minerals
that are essential and often in short supply to
enable technological changes (e.g., electrification of
transportation grid) in modern society.

mineral definition

A mineral is a naturally occurring solid with a
highly ordered atomic arrangement and a
definite, but not necessarily fixed,
homogeneous chemical composition. It is usually
formed by inorganic processes.

mafic vs felsic

mafic- dark and heavy (iron, magnesium, calcium)

felsic- light and light, lower temp (oxygen, silicone)

uses for mineralogy

geophysics, structural geology, geochronology, petrology, geochemistry, planetary studies, paleontology, marine science, environment science, economic geology, medical geology, mineral physics

quantum numbers

atomic vs ionic radii

to make up the right number of electrons, use elements of same size thats interchangeable such as nickel and magnesium

ionic radius

higher positive charge means less atomic radius, lower charge means more atomic radius

ionic bonding

forms when
one or more electrons in
the valence shell of an
atom are transferred to
the valence shell of
another so that both
elements achieve an inert
gas configuration

different bonds have different strengths and different melting points

e.g. halite

covalent bonds

orms when two
(or more) atoms share their outer
valence electrons (overlap of
orbitals) to achieve the stable
noble gas configuration.

e.g. diamond

metallic bonds

forms when
positively charge atomic nuclei share
electrons in their electron clouds
freely. In a sense, each atom is
sharing electrons freely with other
atoms, and some of the weakly bound
electrons are free to move from
atom to atom.
e.g. copper and pyrite

residual bonds

are weak bonds
that involve the attraction of partially charged atoms or
molecules. These partial charges are created when
electrons become concentrated on one side of an atom or
molecule to satisfy ionic or covalent bonds.

e.g. graphite

Van der Waals

type of residual bond that form by polarisation of residual charges

hydrogen bonds

an electrostatic bond between a
positively charged hydrogen ion and a negatively charged
ion, such as O2- or N3-.

crystaline

Crystaline (often spelled crystalline) is a common spelling variant that generally refers to being made of or resembling crystal, clear, or structured in a repeating atomic pattern

crystalinity

disorder and instability

order and instability

order and stability

how the ions interact with eachother

crystal structure

Crystal structure controls physical properties such
as cleavage, hardness, density, melting point, index
of refraction, etc.
• The nature of the
chemical bonding is the primary
control on crystal structure.
• Cations and anions can be thought of as spheres of
different sizes (i.e., representing different
elements), although this is of course a gross
oversimplification.
• Packing of metals: element(s) with (approximately)
the same size, very ordered packing that minimizes
void space (
closest packing).
• Packing of elements with different size: in general,
the smaller cations fill the voids in the closed-
packed array of larger anions (ionic bonding); they
are said to be
coordinated.

closest packing

hexagonal closest packing (HCP)

Face centred cubic closest packing (CCP)

coordination of ions

Paulings Rules: Rule 1 Coordination Principle

Rule 2: Electrostatic valency

In a stable ionic structure, the total strength of the valency
bonds that reach an anion from all neighboring cations is equal to
the charge of the anion.

Rule 3: Sharing of Polyhedral elements

The existence of edges and particularly faces decreases the
stability of ionic structures.

Rule 4: Sharing of polyhedral elements II

In a crystal containing different cations, those of high valence
and small coordination number tend not to share polyhedral
elements with each other

Rule 5: Rule of parsimony

The number of essentially different kinds of constituents in a
crystal tends to be small.

crystallography

Crystallography is the study of the external form and
internal atomic arrangement of crystalline solids and the
principles that govern their growth, external shape, and
internal structure.

symmetry

– Translation symmetry: repetition of a motif through a volume.
– Point symmetry: repetition of a motif around a point.

repetition of objects through roation, reflection, inversion and translation

repeat unit cells

The 6 crystal systems

common symmetry elements

Miller indicies

1 if its touching, 0 if its parallel

isometric systems

equal measurement

non-isometric systems

can be combined with isometric but must be compatible

euhedral, subhedral & anhedral.

• Euhedral (also called idiomorphic): Crystals that are completely well-formed with sharp, easily recognized, and fully developed faces. This happens when a crystal grows freely in an uncrowded environment like a liquid melt or a vug (cavity) with plenty of space. [1, 2, 3, 4]

• Subhedral (also called hypidiomorphic): Crystals that show an intermediate form, having some well-developed faces mixed with irregular or incomplete faces. [1, 2]

• Anhedral (also called xenomorphic): Mineral grains that have no smooth external crystal faces or regular geometric shapes at all. This occurs in crowded, competitive environments where growing crystals bump into each other and run out of free space. [1, 2, 3]

microscope diagram

wave properties

polarisation only allows EW light

phase and retardation

Velocity of light changes depending on the medium (will change going through the crystal), frequency will tend not to change

so for example it will be slower in glass than air because the glass is denser. glass has more intereference because it is thicker

relief

degree to which a mineral stands out from the mounting medium

becke line

lower and lift the platform, and if the bright line goes in when you lower the stage- the one it goes into is higher density

light polarisation

colour and pleochroism

Colour: the wavelength that is not absorbed by the mineral
Pleochroism: change in colour (PPL) as stage is rotated

true colour: what you can see with your eye

isotropic- no pleochroism

anisotropic unixial- yes or no, if yes 2 colours

anisotropic biaxial- yes or no, if yes 3 colours

isotropic vs anisotropic mineral

Isotropic materials – the velocity of light is the same in all
directions (gases, liquids, glasses, minerals in the isometric
system).
- Single refractive index

Isometric

the colour wont change in ppl, will be extinct at 90 in xpl

Anisotropic materials – the velocity of light changes
depending on the orientation direction (crystals in the
tetragonal, hexagonal, orthorhombic, monoclinic, triclinic
systems).
- Light is broken into two polarized rays with different
velocities vibrating at right angles
- More than one refractive index

• double refraction like in calcite

• may change with stage rotation in ppl, interference colours in xpl

• the dot that looks ‘deeper’ is the slower vibration

retardation

The light entering the mineral
with thickness
d is split into
slow and fast rays. In the time
it takes the slow ray to pass
through the mineral, the fast
ray will have traveled through
the mineral plus an additional
distance Δ, which is the
retardation.

birefringence

The birefringence value depends
on the path followed the light
through the mineral. Some paths
(i.e. along optical axes) show zero
birefringence, others show
maximum and most are
intermediate

birefrigencexthickness=retardation

to measure, make the crystal parallel to plane of light

interference colours

Each wavelength will be
split into fast and slow
rays.
• Depending on thickness and
orientation, rays for some
wavelengths are
transmitted and some are
cancelled in the analyzer.
• The combination of
transmitted wavelengths is
perceived as interference
colours.

extinction

parallel

inclined

symmetrical

none

isotropic are always extinct, anisotropic should do extinct every 90 degrees

habit

nature and texture

can also be prismatic

form

interaction with light

• Transparent: transmits light and through which an object may be seen. 

• Translucent: capable of transmitting light diffusely but is not transparent. 

• Opaque: does not transmit light, even on thin edges. 

lustre

hardness

scratch test

cleavage and fracture

index of refraction

the velocity of light in air but also in mineral, n being less than one means it has a higher frequency than light (very unlikely). Remember the n numbers for different minerals

a mineral will stand out if it has a higher refractive index

isotropic vs anisotropic uniaxial and biaxial

uniaxial negative and positive

birefingence of uniaxial minerals

uniaxial positive interference figure

try to find a crystal that is extinct all the time when polars are crossed, the triangle

uniaxial negative interference figure

elongation

biaxial negative and positive

light travel relationship

denser material- further to travel, slower velocity, higher refractory index, more colour absorption, brighter colour

faster light=smaller refractory index

ordinary vs extraordinary rays

ordinary rays= look down optic axis, look from the top, more colour, ‘the triangle’, c axis perpendicular

extraordinary rays= side/elongated, extinct with rotation, c axis parallel

biaxial interference figure positive

biaxial interference figures negative

optic axis

where i look on the crystal and only see one velocity. it will go extinct when you cross the polars.

coordination number of an element

ratio of anions to cations

olivine under microscope

Equant- grows approx the same amount in all directions

Curved fractures

Will appear white

Yellow lines (alteration), serpentine

High interference colours with polarised plate (very colourful) with high order colours like bright yellow

feyeyalite vs fosterite

fayalite has more iron compared to magnesium in it which makes it denser, fayalite has a higher refractive index because it slows down the light, bigger biorefringence

mantle vs crust composition

mantle- 35km down

denser material closer to core, nickel and iron rich

oxygen bonds to silica, hence in crust and mantle

olivine chemical formula

(Mg,Fe)2SiO4

can also contain calcium (ca)

pyroxene formula

SiO3 with mf or fe

weak beams on diagonal causes cleavage

pyroxene classification

amphibole

double chains

Z8O22(OH)2

amphibole classification

minerals in olivine

Orthopyroxene is the darker mineral in the green

clynoperoxyne= grass green, looks like emeralds

olivine is the light green

Basalt is on the outside

spinel vs serpetine

Spinel= high relief, cubic, isotropic, bright yellow

Serpentine= in the racks, duller yellow, low relief

olivine with rust

Olivine breaks down by becoming red (iron)

Iron (2+) doesn't like oxygen,

has to add to 2 with si04, mostly iron could be fe1.6 mg0.4 si04

Rust= feOOH

Red in new caledonia because of the rust, magnesium that is leached in rust goes to coral reef, in central qld its white because the magnesium becomes magnesium carbonate

pyroxene hand sample

Density (heavy), environment, can appear bronze, dark

Will kind of have large grains, black lines intersect

 

clino vs orthopyroxene

One will be colourful (high interference colours) (clino), and the other will be grey or have low interference colours (it can go to second order rarely) (ortho)

clino will also go extinct in a different position

amphibole look

Shiny, long, black, larger

Colour zonation

Grain Shape: long

Relief: high

 

Colour: strong colours (yellow, green, pitch black), can have twinning, tri chroism (three different shades of colour is a characteristic), can also have zoning

 

Pleochroism: kind of

 

Interference colours: not very high

 

Birefringence:

 

Retardation:

 

Extinction: on angles?

 

Cleavage: 60 degrees and 120 in another (form an angled criss cross)

 

Other:

 

olivine in thin section

First look for relief then for interference colours

If you add water to orthopyroxene, serpentine will appear, similar base chemical formula

 

Grain Shape: orthorhombic, look like rounded rectangles

Relief: high, (the n numbers are high on the slides)

 

Colour: clino will often have twinning (two colours with a band in between), generally yellowey grey

 

Pleochroism (rotating without the polariser): no

 

Interference colours: ortho, first order, clino, higher order

 

Birefringence: low?

 

Retardation: high?

 

Extinction: when lines are facing NS, will go extinct on a 45 degree angle

 

Cleavage: straight/linear

 

Other:

 

triclinic

1 one fold with or without inversion

monoclinic

1 two-fold and or one mirror plane

orthorhombic

3 two fold and or 3 mirror planes

tetragonal

1 four fold

trigonal hexagonal

1 three fold

hexagonal

1 six fold

isometric

4 three fold

pinacoid

flat surface, applies to hexagonal and tetragonal prism

enstatite

MgSiO3

Ferrosilite

FeSiO3

Diopside

CaMgSi2O6

Hedenbergite

CaFeSi2O6

ionic radius of Mn, Fe, Co, Ni, Mg

0.6-0.8

ionic radius of Ca

1.0