Amateur Geologist Structured Geological Glossary: Geochemistry

Structured Geological Glossary: Geochemistry

geochemistry	A branch of geology that focuses on the chemical composition of Earth materials.
biogeochemistry	The chemical interactions among the atmosphere, biosphere, hydrosphere and lithosphere. Study of the cycling transformations and transport of chemicals in and between landscapes and ecosystems.
trace element	An element that appears in mineral in a concentration of less than l percent (often less than 0.001 percent).
ion	An atom or group of atoms that has gained or lost electron and so has a net electric charge.
cation	Any ion with a positive electric charge.
cation exchange capacity	Sum total of exchangeable cation retained by negatively charged soil particles. Units of milliequivalents per 100 grams of soil. Abbreviated CEC.
oxidized element	An element occurring in the more positively charged of two common ionic form.
carbonate	A sedimentary rock made mainly of calcium carbonate (CaCO3). Limestone and dolomite are common carbonate sedimentary rocks.
silica	Silicon dioxide (SiO2). One of the most common compounds in the Earth’s crust. Common window glass is made of silica. The building block of the mineral quartz and other silicate minerals.
silicate	Refers to the chemical unit silicon tetroxide, SiO4, the fundamental building block of silicate mineral. Silicate minerals make up most rocks we see at the Earth’s surface.
nonsilicate minerals	A mineral without silicon (Si).
inorganic	Obtained from mineral, not organic.
alkali metal	A strongly basic metal like potassium or sodium.
chemical sediment	A sediment created by precipitation of one or more mineral from natural waters.
reversible reaction	A chemical reaction which can proceed in either direction, depending on the concentration of reacting materials.
large-ion lithophile elements	Elements with an affinity for oxygen-containing compounds, particularly silicate mineral, and possessing ionic radii larger than most common rock-forming elements. Examples include K, Cs, Th, U, La, Ba.
abundance	O 46.6 Mg 2.09 Si 27.62 Ti .044 Al 8.13 H 0.14 Fe 5.00 Mn 0.1 Ca 3.63 Mn 0.1 Na 2.83 S 0.05 K 2.59 C 0.03
hydrolysis	A chemical reaction between water and another chemical compound such as a mineral. For example, water reacts with orthoclase to form the clay mineral kaolinite.
volatile	Elements that are soluble in magma at elevated pressure and temperature that exsolve as gas from magmas during ascent and eruption at the earth's surface. They include sulfur, water, carbon dioxide, chlorine and fluorine.
precipitation	Any condensed water falling from the atmosphere to the surface of the earth. Common types include rain, snow, sleet and hail.
soft mode	Molecular vibrational mode for which the atomic displacement track the structural changes followed during a displacive phase transition. The frequency of the soft mode goes to zero at the transition temperature or pressure.
sublimation	The direct change from the solid to the vapor phase (without passing through the liquid phase). Commonly occurs in ice and snow fields on sunny days above the snowline.
gas-to-particle reaction	The formation of particles by the rapid condensation of a gas.
thermophile	Solute diffuses into warmer bottom waters.
isotope	One of two or more atom that have the same atomic number (i.e., the same number of protons in their nuclei) but have different mass numbers. Forms of the same element that have the same number of protons but differing numbers of neutron. This mass difference gives rise to slightly differing chemical properties for each isotope. Of interest here are the stble isotopes of carbon: carbon-12 (or 12C) and carbon-13 (or 13C), which are stable over time and carbon-14, which is a radioisotope and decays with time to an isotope of nitrogen.
cosmogenic isotope	Isotope produced by nuclear reactions induced by cosmic-ray particles.
half-life	The time required for half of a homogeneous sample of radioactive material to decay.
parent element	An element that is transformed by radioactive decay to a different (daughter) element.
parent element	A radioactive element that changes to a different, daughter element when its nucleus decays.
daughter element	Also daughter product. An element that occurs in a rock as end product of the radioactive decay of another element.
daughter element	An element produced by decay of a radioactive parent element.
closed hydrochemical system	Physical portion of the earth in which the mass of a given immobile chemical element remains constant throughout a chemical and physical transformation process and is enriched only by removal of mobile elements.