introduction mineralogy geol 3010ruby.colorado.edu/~smyth/g3010/lecture1.pdfdefinition of a mineral...
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GEOL 3010Mineralogy
Introduction
Logistics
• Joseph R. Smyth• Office: 340 Benson• Office Hours 10:30-11:30 TTh• http://ruby.colorado.edu/~smyth/syl3010.html• http://ruby.colorado.edu/~smyth/Home.html
Why Study Minerals?
• Minerals are the way atoms are arranged inrocks.
• Atomic environments in rock arehomogeneous from the mm scale to the Åscale (8 orders of magnitude).
Rocks are aggregates of minerals.
Minerals are homogeneous downto atomic scale.
Definition of a Mineral
• A mineral is a naturally occurring,homogeneous solid with a definite, but notfixed composition, and an ordered atomicarrangement that is formed by inorganicprocesses.
• A mineral is a natural, crystalline phase.
Minerals are Naturally Occurring
• In order to be a mineral, a chemicalcompound must occur naturally somewhereand be stable enough to study in the lab.
• We can make many compounds in the labthat are not minerals unless they are foundin nature.
Mineral are homogeneous
• Minerals are chemically homogeneousdown to the atomic scale.
Definite, but not fixed, composition.
• Minerals have chemical formulas determinedby the atomic structures.
• Symmetry requires atoms to occur in simple,specific, integer ratios.
• But, for a given mineral, substitutions ofsimilar elements are possible.
Ordered atomic arrangement
• Minerals are crystals.• Crystals are periodic arrays of atoms.• Atoms achieve their lowest energy by
having the each different type of atom(element) in an identical environment.
Inorganic Processes
• The mineral must have at least oneoccurrence where it is formed by inorganicprocesses.
• Calcite may be formed by organisms toform shells, but it does also occur inigneous and metamorphic environments.
These are Minerals
• Gold, silver, diamond, graphite• Pyrite, marcasite, sphalerite• Salt (halite), fluorite, calcite, apatite• Olivine, garnet, zircon• Pyroxene, amphibole, mica• Quartz, feldspar, zeolite
These are NOT Minerals
• Granite, basalt, limestone (rocks)• Wood, coal (organic, non-crystalline)• Opal, obsidian, pumice (non-crystalline)
Polymorphs
• Two minerals with the same composition, butdifferent structures are different minerals.
• Diamond and graphite are both pure carbon,but are different minerals
• Quartz-tridymite-cristobalite-coesite-stishovite all SiO2.
• Calcite-aragonite.
Isomorphs
• Minerals with the same structure anddifferent compositions are isomorphs.
• Forsterite (Mg2SiO4) and fayalite(Fe2SiO4) are isomorphs.