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Natural Science II – ERTH 1040
Solid Lithospheric Phases
J. D. Price
Very important questions:
What are the elements that make up the
entire Earth?
From where did they come?
Minerals
What are those found in the crust?
The latter will be more important for the
Earth’s surface
Bulk Earth
Crust
Q: How do we know these diagrams
(hint: pieces of asteroids)?
There are 90 Natural Elements
Only a few elements occur as single atoms in
nature (Col VIIIA). Most are bonded to other atoms
through
•Interactions with electrons
•Ionic (atomic) charge (+ attracts -)
Single elements may bond to each other (H-H, N-N,
Au to a bunch of other Au , Same with Ag).
Minerals
Boded atoms make molecules.
These are compounds (polyatomic materials)
Q: What are the elements of column
VIIIA on the periodic table?
While not all elements are able to combine, there
are millions of compounds
But a much smaller number occur in nature
Even a smaller number occur near the surface of
the Earth. What limits the number?
Consider this:
Ca + O = CaO
Minerals
More energy* Less energy*
CaO+ SiO2 = CaSiO3
*At near-surface temperatures
and pressures
Energy is the universal currency, and nature appears
to be on a budget
The Earth is a dynamic place, conditions change
(e.g. T,P) for materials on the move. What may be
the lowest energy form deeper in the earth may be
excessive near the surface.
Therefore, changes in compounds are possible.
Please note: change is never instantaneous,
requires time and/or additional energy.
Minerals
Example: you place a small ice cube at 0 oC into
water at 25 oC
H2Oice = H2Oliq
Ice takes a few minutes to become liquid and
consumes heat to do so.
Two terms that describe a compound
Composition: the number of atoms of each element
present in a compound
CaSiO3: one Ca for every one Si and three O
Structure: how the atoms are bonded to one another
CaSiO3: one Ca bonded to a O, bonded to one Si,
bonded to three O…
A compound with consistent properties (composition &
structure) is a phase:
CaO, SiO2, and CaSiO3 are different phases
H2O as a liquid is a different phase than H2O as a solid
If these are the elements of the
crust – what compositions are
most likely to be present?
Some chemical nomenclature
MO (metal oxygen) oxide
e.g. CaO = calcium oxide
MNO (metal-nonmetal-oygen)
nonmetalate
e.g. CaSiO3 = Calcium silicate
Q: Which of the above elements are metals and
nonmetals (including semiconductors)?
Metals (M) prefer to lose electrons
Major structural differences
Recall the states of matter: gas, liquid, solid.
Solid Earth scientists typically use the following
nomenclature for structural phase types:
“fluid” liquid or gas
“glass” solid, but not crystalline
Minerals
“mineral” solid and crystalline
Crystalline
CsCl
Crystalline
SiO2
Glass
SiO2
Solid structures
Crystalline solids are made of strongly bonded
atoms. Compounds may have different structural
arrangements given energy constraints.
Ideally, scientists apply different names to phases
of different solid structures
Minerals
Example: Ice I (low pressure) vs. Ice II (higher
pressure) – see hydrologic cycle notes
Q: why no mention of different
structures in liquids or gasses?
Examples of structure
High resolution transmission
electron image of a pyroxene.
Scale bar is 0.88 nm. Bright
areas have fewer atoms.
From Klein and Hurlbut, 1999
High resolution transmission
electron image of an anatase.
Scale bar is 0.88 nm. Spheres
are topography on O atoms.
Note repetition of pattern in 2D
in both images. The repeated
occurrence of atoms is called
a lattice.
Penn and Banfield, 1999
Bringing atoms together –
Several structures that result from two things:
The bonds between atoms
Minerals
The size of each atom
Halite - NaCl
Fluorite – CaF2
Q: What ultimately
controls structure?
Looking at NaCl
Note alternating Na and Cl
atoms (1 Na for every 1 Cl)
There is a bond (electron
movement and charge
attraction) holding each Na
to each Cl: outlining this
makes a cubic pattern
We may also outline the relationship
between atoms. 1 Na is attached to 6
nearest Cl: octahedron
These two subsets of the above
model are the same with respect to
bonding
When atoms are bonded together in repeating
lattices, they build geometric shapes
Image from Perkins, 1998
Controls on external shape
What makes a bubble round?
Could those same forces work for crystals?
Penn and Banfield, 1999
What’s the difference
between this atom
And this one
The greater anisotropy of the structure,
the more this is a problem!
Minerals
Q: Which is the more stable
configuration of 36 atoms?
Minerals
From Blackburn &
Dennen, 1998
Growth Facets
Minerals
Polished Facets
Basic structure for silicate
minerals
Minerals
Bond model
Outline models
Because each Si is surrounded by four O,
the outline shape is a tetrahedron
Q: Where are Si and O on the
periodic table?
Isolated silicate tetrahedra
Minerals
-2
+2
Q: Where might we find additional
elements in this structure?
Isolated silicate tetrahedra
Olivine
(Mg,Fe)2SiO4
Minerals
Garnet
(Mg,Fe,Ca)3(Al,Fe,Cr)2 SiO4
Image from mineral.galleries.com
Single chain of tetrahedra
-4
Top
+2
Side
Top
Q: where are the non-silicate components in this structure?
Single Chain Silicate Tetrahedra
Pyroxene
(Mg,Fe)2Si2O6
Ca(Mg,Fe)Si2O6
Minerals
Wollastonite
Ca2Si2O6
Image from mineral.galleries.com
Double chain of tetrahedra
-4
Top
+2
Side
Top
Q: where are the non-silicate components in this structure?
Double Chain Silicate Tetrahedra
Wollastonite
(Ca,Mg,Fe,Al)6-7(Al,Si)8O22(OH,F)2
Minerals
Amphibole Asbestos
Crocidolite
Na2Fe2+3Fe3+2(Si8O22)(OH)2
Image from mineral.galleries.com
Sheet structure silicates
Minerals
Top
Side
Q: where are the non-silicate components in this structure?
Sheet silicate
Muscovite
KAl2(AlSi3O10)(OH,F)2
Biotite
K(Mg,Fe)3(AlSi3O10)(OH,F)2
Phyllosilicate Asbestos
Chrysotile
Mg3(Si2O5)(OH)4
Q: Is all asbestos the same?
Image from mineral.galleries.com
Framework silicates
Minerals
Top
Side
Q: where are the non-silicate components in this structure?
Framework Silicate Tetrahedra
Feldspar
SiO2
Feldspar
(Ca,Na,K,Al)(Al,Si)3O8
Q: What is unique about the
structure of framework
silicates?
Images from mineral.galleries.com
Other important (but less abundant) nonmetals
Carbon, Sulfur, Chlorine
Carbonates (MCO3)
Calcite CaCO3
Sulfates (MSO4)
Anhydrate CaSO4
Gypsum CaSO4 2H2O
Halides (MH) metalhalogen (F, Cl)
Halite NaCl
Images from
mineral.galleries.com
Of course you can combine a single
nonmetal with a metal
Oxides (MOx)
Magnetite Fe3O4
Minerals
Sulfides (MSx)
Pyrite FeS2
Image from mineral.galleries.com
Q: Why are these are
called ore minerals?
Single element solids
Native Elements
Gold
Silver
Diamond
Graphite
Sulfur
Au
Ag
C
C
S
Minerals
Great Ores – little to no refining
involved, but very limited in
availability
Images from
mineral.galleries.com
We’ve mentioned a number of minerals
Know:
What two elements are present in each 1.)
silicate, 2.) sulfate and 3.) carbonate.
The different structures of silicates
What type of element is present in halides
What element must be present in 1.) oxides and
2.) sulfides
What makes a native element mineral
Minerals
Keep these notes handy:
Know where to find the specific minerals named
and their composition.