Solid Lithospheric Phases J. D. Price Very important questions: - - PowerPoint PPT Presentation

Solid Lithospheric Phases

• J. D. Price

Natural Science II – ERTH 1040

Minerals

Very important questions: What are the elements that make up the entire Earth? From where did they come? 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)?

Minerals

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). Boded atoms make molecules. These are compounds (polyatomic materials) Q: What are the elements of column VIIIA on the periodic table?

Minerals 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

More energy* Less energy*

CaO+ SiO2 = CaSiO3

*At near-surface temperatures and pressures

Minerals 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. 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. Energy is the universal currency, and nature appears to be on a budget

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

Minerals 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 “mineral” solid and crystalline

Major structural differences

Crystalline CsCl Crystalline SiO2 Glass SiO2

Minerals

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

• f different solid structures

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?

From Klein and Hurlbut, 1999

Examples of structure

High resolution transmission electron image of a pyroxene. Scale bar is 0.88 nm. Bright areas have fewer atoms.

Penn and Banfield, 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

• ccurrence of atoms is called

a lattice.

Minerals Bringing atoms together – Several structures that result from two things: The bonds between atoms 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

Image from Perkins, 1998 When atoms are bonded together in repeating lattices, they build geometric shapes

Penn and Banfield, 1999

What makes a bubble round?

Controls on external shape

Could those same forces work for crystals? 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

Minerals Growth Facets Polished Facets

Minerals Bond model Outline models

Basic structure for silicate minerals

Because each Si is surrounded by four O, the outline shape is a tetrahedron Q: Where are Si and O on the periodic table?

Minerals

Isolated silicate tetrahedra

Q: Where might we find additional elements in this structure?

• 2

+2

Minerals

Isolated silicate tetrahedra

Olivine (Mg,Fe)2SiO4 Image from mineral.galleries.com Garnet (Mg,Fe,Ca)3(Al,Fe,Cr)2 SiO4

Single chain of tetrahedra

Top Side

• 4

+2 Top

Q: where are the non-silicate components in this structure?

Minerals

Single Chain Silicate Tetrahedra

Image from mineral.galleries.com Pyroxene (Mg,Fe)2Si2O6 Ca(Mg,Fe)Si2O6 Wollastonite Ca2Si2O6

Top Side

Double chain of tetrahedra

• 4

+2 Top

Q: where are the non-silicate components in this structure?

Minerals

Image from mineral.galleries.com

Double Chain Silicate Tetrahedra

Wollastonite (Ca,Mg,Fe,Al)6-7(Al,Si)8O22(OH,F)2 Amphibole Asbestos Crocidolite Na2Fe2+

3Fe3+ 2(Si8O22)(OH)2

Minerals Top Side

Sheet structure silicates

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 Image from mineral.galleries.com Phyllosilicate Asbestos Chrysotile Mg3(Si2O5)(OH)4

Q: Is all asbestos the same?

Minerals Top Side

Framework silicates

Q: where are the non-silicate components in this structure?

Feldspar (Ca,Na,K,Al)(Al,Si)3O8 Images from mineral.galleries.com Feldspar SiO2

Framework Silicate Tetrahedra

Q: What is unique about the structure of framework silicates?

Other important (but less abundant) nonmetals Carbon, Sulfur, Chlorine Carbonates (MCO3)

Calcite CaCO3

Sulfates (MSO4)

Anhydrate CaSO4 Gypsum CaSO4 2H2O

Halides (MH) metal- halogen (F, Cl)

Halite NaCl Images from mineral.galleries.com

Minerals Of course you can combine a single nonmetal with a metal Oxides (MOx)

Magnetite Fe3O4

Sulfides (MSx)

Pyrite FeS2 Image from mineral.galleries.com

Q: Why are these are called ore minerals?

Minerals Native Elements

Gold Au Silver Ag Diamond C Graphite C Sulfur S Images from mineral.galleries.com

Great Ores – little to no refining involved, but very limited in availability

Single element solids

Minerals 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 Keep these notes handy: Know where to find the specific minerals named and their composition.