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PE I & Geo I – ERTH 1010 & 1100. Solid Lithospheric Phases. J. D. Price. Minerals. Naturally occurring Crystalline Inorganic Materials. Not man made Symmetric atomic lattice Not life compounds. Cartoon atoms. Not an accurate picture Electrons too large and too close to nucleus
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PE I & Geo I – ERTH 1010 & 1100 Solid Lithospheric Phases J. D. Price
Minerals • Naturally occurring • Crystalline • Inorganic • Materials • Not man made • Symmetric atomic lattice • Not life compounds
Cartoon atoms Not an accurate picture Electrons too large and too close to nucleus Movement is not oval Distribution is trickier Recall Z defines the behavior of the atom (makes it elemental) N can vary for an element (isotopes) Example 12C = 6N + 6Z , 14C = 8N + 6Z
Atoms • Electron • Neutrons • Proton Mass 9.109 E -31 kg 1.673 E -27 kg 1.673 E -27 kg Charge (-) 1.602 E -19 coul. (0) None (+) 1.602 E -19 coul. Electrons are attracted to protons because opposite charges attract. The number of protons dictates the maximum number of electrons - each element has a limit to the number of electrons The electrons control the behavior of the atom - each element behaves differently
s orbitals, l = 0 p orbitals l = 1, m = -1,0,1 d orbitals l = 2, m = -2, -1, 0 , 1, 2 f orbital l = 3 m = -3, -2, -1, 0, 1, 2, 3
Ions Atoms may lose electrons They become ions! We note the charge difference in integers (e.g. +1) For many atoms, the first electron is easy to remove, but additional electrons are not.
Single Electron (hydrogen atom) Multiple electron* *exact energies vary with Z
Ionic bonding A few elements can add electrons (right side of periodic table). This makes negatively charged ions that may attract positive ones. Can only attract so far – “solid spheres”
Neutral Atom Size Decrease across a period. Increase down a group When moving across a period of main group elements, the size decreases because the effective nuclear charge increases.
Covalent bonding Two hydrogen atoms in close proximity can share their electrons so that each takes on an electronic structure similar to He – a noble gas. The diatomic H-H system:
There are 90 Natural Elements • Only a few elements occur as single atoms in nature (Col VIIIA). Most are bonded to one or more other atoms through: • Interactions with electrons • Ionic (atomic) charge (+ attracts -) • Single elements may bond to each other entirely covalently. • Compounds (two or more elements) attach through a combination of ionic and covalent bonding. • Boded atoms make molecules, chains, or lattices. • These are compounds (polyatomic materials)
Composition Bulk Earth Crust These are the elements from which we can make compounds - combinations of elements. Most minerals are made of these.
Energy controls it all 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
Work and Energy Applying a force (or pressure) may result in motion. This force through a distance is known as work. Energy is the quantifiable ability to do work. Energy = Work = Force x distance = mass x acc. x dis
Units of Energy • The Joule is Nm or kg m2 / s2 or the energy needed to move a charge of 1 coulomb through a potential of 1 volt • 1 joule is approximately equal to: • 6.2415 ×1018 eV (electronvolts) • 0.2390 cal (calorie) (small calories, lower case c) • 2.3901 ×10−4 kilocalorie, Calories (food energy, upper case C) • 9.4782 ×10−4 BTU (British thermal unit) • 2.7778 ×10−7 kilowatt hour
A force applied in doing work goes into overcoming a resistance, which causes a change in energy...
Energy operates at all scales! It is the universal term in our current physical understanding of nature. The energy in gravitationally driven galaxies The energy that binds subatomic particles. The primary rule (First Law of Thermodynamics): energy cannot be created or destroyed. It must be converted. In any system, you have what you have. Like accounting - you can keep track of conversions but the total never changes.
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 oC into water at 25 oC H2Oice = H2Oliq Ice takes a few minutes to become liquid and consumes heat to do so.
Compounds • 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-oxygen) nonmetalate e.g. CaSiO3 = Calcium silicate Q: Which of the above elements are metals and nonmetals (including semiconductors)?
Metals, nonmetals, 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 Crystalline SiO2 Glass SiO2 Crystalline 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 Q: why no mention of different structures in liquids or gasses?
Examples of structure 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. Note repetition of pattern in 2D in both images. The repeated occurrence of atoms is called a lattice. Penn and Banfield, 1999
Transmitted Electron Microscopy TEM sends electrons through a thin film of the mineral. Electrons are stopped by the atoms. High-resolution TEM uses interference of the electron interaction with the material.
Bringing atoms together – • Several structures that result from two things: • The bonds between atoms • The size of each atom Fluorite – CaF2 Halite - NaCl Q: What ultimately controls structure?
A pinch of 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
The energy available for reactions is known as Free Energy Depends on 1. The nature of the bonding 2. Pressure 3. Temperature 4. Degree of disorder
The Carbon System Graphite - steep dG/dP Diamond - higher initial G, shallow dG/dP
Diamond’s excited state Image modified from Zoltai and Stout, 1984
Crystalline Carbon A soft material Graphite The Hardest material Diamond
Why can we observe graphite and diamond at the same time? There is a place where both phases share the same G, but at room T, this is ~14 kbar (14,000 x atmospheric)!
Phase Diagram Recall that as you go into the Earth, both P and T increase These two variables control phase stability of compositions in the earth. On the left is a map for phases of carbon
Hardness The variety of bonding between elements gives individual minerals an unique hardness. Mohs hardness scale provides a useful relative comparison among common minerals
Cleavage Lattices that are strongly bonded in two dimensions but are weak in one break into sheets. Graphite and micas (right) are two examples of minerals with sheet cleavage Cleavage is the official term given to a minerals ability to break along a lattice plane.
Fracture Some minerals do not easily break along a plane(s). The result is fracture.
Habit When atoms are bonded together in repeating lattices, they build geometric shapes. Common shapes are known as habits Image from Perkins, 1998
Common habits in minerals Cube Octahedron Prism and pinacoids Hexagonal prism and pyramid Dodecahedron Orthorhombic prism and pinacoid Rhombohedron Prism All of this controlled by two parameters: The internal organization of the atoms The energy between the surface and the surrounding medium.
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!
