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.