GeologyRocks

Gangue

The unwanted material around ore minerals

Gardar Province

Geological area of south-west Greenland famous for its alkali intrusions especially Ilimaussaq which has over 200 minerals associated.

Definition provided by: Tim Ivanic (University of Edinburgh)

Garnet

A cubic mineral of the general form of:

A₃²⁺B₂³⁺Si₃O₁₂

A can be magnesium, iron, manganese or calcium, B is iron or aluminium (occasionally chromium). Commonly found in metamorphic and occasionally igneous rocks.

Gene Flow

The incorporation of genes into the gene pool of one population from one or more other populations.

Genetic Bottleneck

A severe, temporary reduction in variation in a population.

Genetic Drift

Random changes in the frequency of two or more alleles or genotypes within a population.

Genotype

The genetic makeup, as distinguished from the physical appearance (phenotype), of an organism or a group of organisms.

Geophysics

A branch of geology where non-invasive techniques such as magnetics, gravity surveys and seismic surveys are used to map unseen geological structures, such as faults.

Gibbs Free Energy

Chemical reactions can be made to do work (e.g. produce heat). Energy which is, or which can be, available to do useful work is called Gibbs free energy (G).

G = H - TS

Where H is the enthalpy, S is the entropy, and T is the absolute temperature.

Gneiss

Metamorphic rock, showing distinct banding of light and dark minerals. Usually made of feldspars, micas and hornblende.