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Fall - a meteorite that was observed to fall from the sky as a meteor; the date of the meteorite's arrival on Earth is known.

Find - a meteorite that was simply found lying on the ground; the date of the meteorite's arrival on Earth is unknown.

Element - a fundamental unit of matter.  An element is a substance that cannot be separated into other substances by any chemical reaction.  For example, water (which is NOT an element, but rather a molecule) can be chemically separated into hydrogen and oxygen (both elements).

Atom - the smallest amount of an element that can exist.  The elemental identity of an atom is determined by the number of protons in the atom's nucleus.  For instance, to be the element carbon, an atom must have 6 protons in its nucleus.

Lithophile element - an element that tends to form chemical bonds with oxygen, typically forming silicate or oxide compounds (minerals).

Siderophile element - an element that tends to bond with iron or other siderophile elements to form metallic alloy compounds (minerals).

Chalcophile element - an element that tends to bond with sulfur, typically forming sulfide compounds (minerals).

Figure from http://www.science.uwaterloo.ca/earth/waton/5a.html  Periodic table of the elements showing chemical affinities.

Petrology - the branch of geology that studies the origin, occurrence,  and chemistry of rocks.

Petrography - the branch of geology that deals with the description and systematic classification of rocks, especially with the use of a microscope.  Petrography is more restricted in scope that petrology.

Mineral - A naturally occurring solid that has a definite chemical composition (chemical formula) and crystalline structure (a regular arrangment of atoms).

Examples of minerals:

Figure from:  http://www.uwgb.edu/dutchs/PETROLGY/Halite%20Structure.HTM -both of these minerals consist of a rectangular arrangement of two atoms (face-centered cubic structure).  The mineral Halite consists of alternating atoms of sodium (Na) and chlorine (Cl), while the mineral Galena consists of alternating atoms of lead (Pb) and sulfur (S)

Polymorph - one of several different crystalline structures that have the same chemical formula.

Example of polymorph:

Figure from: http://www.chem.ufl.edu/~itl/2041_f97/matter/FG11_042.GIF - Diamond and Graphite are two different minerals that are formed solely from carbon (C) atoms.  The difference between a diamond and graphite (which is the lead in a pencil) is the way the atoms are arranged.  We say that diamond and graphite are two polymorphs of carbon.

Rock - an aggregate of minerals.  A rock may be monomineralic (composed of multiple grains of the same mineral) or polymineralic (composed of grains of more than one kind of mineral).

Igneous rock - an igneous rock is a rock that forms by solidification of a melt (magma).  Atoms in the melt come together to form growing mineral grains in a process termed crystallization.

Metamorphic rock - a metamorphic rock is a rock that forms from a previously existing rock by the rearrangement and growth of minerals in the solid state (no melting), in response to changes in pressure, temperature, or fluid composition.  Metamorphic rocks are mainly produced at high temperatures and often at high pressures.

Sedimentary rock - a sedimentary rock is a rock that forms at the surface of a planetary body by processes such as weathering, compaction and cementation. Sedimentary rocks are always produced under conditions of relatively low pressure and low temperature.

Breccia/brecciation - a breccia is a rock made up of angular fragments of one or more pre-existing rocks.  The pre-existing rocks can be broken up into fragments by a number of processes, including impact (shock), shearing along a fault, and explosive volcanic eruptions.  Brecciation is the process of forming a breccia.  For meteorites, brecciation is due to shock (impact).

Figure from:  http://www.gpc.peachnet.edu/~janderso/physical/sedrx.htm - showing a breccia

Refractory element - an element that remains in the solid state (rather than going into a vapor) at relatively high temperatures.

Volatile element - an element that prefers to be in a gaseous state at relatively high temperatures.

Oxidation vs. reduction - oxidation is the addition of oxygen to a chemical compound.  Reduction is the removal of oxygen from a chemical compound.  More generally, reduction involves a decrease in positive valence and oxidation involves an increase in positive valence of an ion.

Ion - an atom that has gained or lost an electron, so that it has a net charge. A positively charged ion is known as a cation; a negatively charged atom is known as an anion.

Valence electron - an electron in the outermost shell of an atom.  For instance, an electrically neutral carbon atom has 6 electrons orbiting a nucleus that contains 6 protons.  Two electrons are in the innermost shell, while the remaining 4 (the valence electrons) are in the outermost shell. It is the valence electrons of an atom that can be lost to form a cation, or swapped with another atom to form a chemical bond.

Valence state refers to whether an atom is in an oxidized or reduced state.  For instance, iron (Fe) is found in rocks in three valence states.  These include (1) reduced iron, in which none of the valence electrons are missing; and two types of ionized iron, (2) Fe2+ - which is missing two valence electrons, and (3) Fe3+, which is missing three valence electrons and is also known as oxidized iron.

Solid solution - this describes the ability of certain minerals to have a range of compositions.  A mineral may have a crystalline structure that allows more than one element to fit into a specific site in that structure, giving rise to compositional variability.  An example of this is the mineral Olivine.  The structure of this mineral consists of units of SiO4 attached to two crystal sites that can contain an element such as iron (Fe) or magnesium (Mg).  In the case of Fe and Mg, olivine forms a solid solution from fayalite [Fe2SiO4] to forsterite [Mg2SiO4].  Fayalite and forsterite are end-members of the olivine solid solution.  In the real world, an olivine grain will typically have a mixture of Fe and Mg filling those two crystal sites, and the formula for olivine is written (Mg, Fe)2SiO4. One can express the composition of an olivine either by the percentage of forsterite (Fo) or fayalite (Fa). Another important solid solution occurs for common pyroxene (Ca,Mg,Fe)SiO3, in which the elements Ca, Mg, and Fe can substitute for one another.  The composition of a pyroxene can be expressed by the endmember proportions it contains of En or enstatite [MgSiO3], Fs or ferrosilite [FeSiO3], and Wo or wollastonite [CaSiO3].  So a pyroxene said to have the composition of Wo5En80Fs15 (or simply Wo5En80, or Wo5Fs15) would have 5% of the wollastonite component, 80% of the enstatite component, and 15% of the ferrosilite component.

Isotope - these are different forms of a particular element which differ in the number of neutrons.  For example, in order for an atom to be an oxygen atom, it MUST by definition have 8 protons in its nucleus, but the number of neutrons can be variable.  Stable isotopes of oxygen are oxygen-16 (8 protons, 8 neutrons), oxygen-17 (8 protons, 9 neutrons), and oxygen-18 (8 protons, 10 neutrons).

Figure from http://www.ims.uaf.edu/isotopes/class-images/isotope-table.jpg - this type of diagram is called a chart of the nuclides, and plots the number of protons (chemical identity) vs. the number of neutrons.  Notice that oxygen has three stable isotopes and five unstable (radioactive) isotopes shown on the diagram.

Devitrification - the solid state transformation of a glass to a crystalline material.