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

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? What are those found in the crust? The latter will be more important for the Minerals Earth’s surface

Crust Bulk Earth 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). Boded atoms make molecules. These are compounds (polyatomic materials) Minerals 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? Ca + O = CaO Consider this: More energy* Less energy* CaO+ SiO 2 = CaSiO 3 Minerals *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. Example: you place a small ice cube at 0 o C into water at 25 o C Minerals H 2 O ice = H 2 O liq 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 CaSiO 3 : 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, SiO 2 , and CaSiO 3 are different phases H 2 O as a liquid is a different phase than H 2 O 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) nonmetal ate e.g. CaSiO 3 = 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 “mineral” solid and crystalline Minerals Crystalline Glass Crystalline SiO 2 SiO 2 CsCl

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 Example: Ice I (low pressure) vs. Ice II (higher pressure) – see hydrologic cycle notes Minerals Q: why no mention of different structures in liquids or gasses?

Examples of structure High resolution transmission From Klein and Hurlbut, 1999 electron image of a pyroxene. Scale bar is 0.88 nm. Bright areas have fewer atoms. 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 The size of each atom Fluorite – CaF 2 Halite - NaCl Minerals 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!

Q: Which is the more stable configuration of 36 atoms? Minerals

Minerals From Blackburn & Dennen, 1998

Growth Facets Polished Facets Minerals

Basic structure for silicate minerals Bond model Outline models Because each Si is surrounded by four O, the outline shape is a tetrahedron Minerals Q: Where are Si and O on the periodic table?

Isolated silicate tetrahedra -2 +2 Minerals Q: Where might we find additional elements in this structure?

Isolated silicate tetrahedra Olivine (Mg,Fe) 2 SiO 4 Garnet (Mg,Fe,Ca) 3 (Al,Fe,Cr) 2 SiO 4 Minerals 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) 2 Si 2 O 6 Ca(Mg,Fe)Si 2 O 6 Wollastonite Ca 2 Si 2 O 6 Minerals 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) 8 O 22 (OH,F) 2 Amphibole Asbestos Crocidolite Na 2 Fe 2+ 3 Fe 3+ 2 (Si 8 O 22 )(OH) 2 Minerals Image from mineral.galleries.com

Sheet structure silicates Top Side Minerals Q: where are the non-silicate components in this structure?

Sheet silicate Muscovite KAl 2 (AlSi 3 O 10 )(OH,F) 2 Biotite K(Mg,Fe) 3 (AlSi 3 O 10 )(OH,F) 2 Phyllosilicate Asbestos Chrysotile Mg 3 (Si 2 O 5 )(OH) 4 Q: Is all asbestos the same? Image from mineral.galleries.com

Framework silicates Side Top Minerals Q: where are the non-silicate components in this structure?

Framework Silicate Tetrahedra Feldspar SiO 2 Feldspar (Ca,Na,K,Al)(Al,Si) 3 O 8 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 (MCO 3 ) Calcite CaCO 3 Sulfates (MSO 4 ) Anhydrate CaSO 4 Gypsum CaSO 4 2H 2 O Halides (MH) metal- halogen (F, Cl) Halite NaCl Images from mineral.galleries.com

Of course you can combine a single nonmetal with a metal Oxides (MO x ) Magnetite Fe 3 O 4 Sulfides (MS x ) Pyrite FeS 2 Minerals Q: Why are these are called ore minerals? Image from mineral.galleries.com

Single element solids Native Elements Gold Au Silver Ag Diamond C Graphite C Sulfur S Great Ores – little to no refining involved, but very limited in availability Minerals 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 Keep these notes handy: Minerals Know where to find the specific minerals named and their composition.