Gauss, Carl Friedrich
German mathematician (1777 - 1855), in the beginning of the 19th century known for his works in physics and mathematics. He did for the first time an absolute measurement of the intensity of the geomagnetic field and a global analysis of the geomagnetic field, called spherical harmonical analysis. He is also known for the law of Gauss, which allows to define an error at a given level of confidence for the estimation of the true mean of a series of observations.

Geographic meridial plane
Plane containing the local vertical and the rotation axis of the Earth.

Geographic north/south pole
Point on the surface of the Earth in the northern/southern hemisphere, situated on the Earths rotation axis. Follow this link to see the definitions of the geographic and the geomagnetic coordinate system.

Geomagnetic field
Magnetic field of the Earth. Resembles the field of a centric magnetic dipole inclined about 11.4° to the rotation axis of the Earth. It is defined in each place at a certain instant of time by its direction (declination, inclination) and intensity. The geomagnetic field is divided in an internal part (the main part), which is caused by fluid movements in the outer fluid core of the Earth and other sources in the upper Earth mantle and the Earth’s crust, and an external part which is caused by currents in the ionosphere and magnetosphere. A complete mathematical description of the potential of the total magnetic field was developed by C.F. Gauss based on spherical harmonics.

Geomagnetic north/south pole
Poles based on a global analysis of the observed geomagnetic field limited to
dipole terms. The geomagnetic poles corresponding to the International Geomagnetic Reference Model (IGRF) of 2005 are situated at:

North geomagnetic pole: 79.7° N and 71.8° W
South geomagnetic pole: 79.7° S and 108.2°E

Follow this link to see the definitions of the geographic and the geomagnetic coordinate system.

Geomagnetic reversal
The phenomenon of polarity change of the  geomagnetic field. Currently, the south magnetic pole is situated in the southern hemisphere and the north magnetic pole in the northern hemisphere (normal polarity). This was not always the case in the Earth's past. If the magnetic poles are oppositely situated compared to now (i.e. the magnetic north pole was in the southern hemisphere) one speaks about reversed polarity. Such polarity switching occurred many times in the geological past. The time between geomagnetic reversals is termed chron. We are presently in the Brunhes chron, called after Bernhard Brunhes (1867-1910). The chron before, when the magnetic poles were oppositely situated compared to now, is called Matuyama, named after Motonori Matuyama (1884-1958). The last geomagnetic reversal, known with certainty, occurred 778 000 years ago and is called Matuyama/Brunhes.

Antiferromagnetic mineral, but exhibits a weak ferromagnetic moment due to defects in the crystal structure. Acicular or fibrous, but in general isometric and of irregular form. Colour: brown-black, yellowish brown to red. In powder form yellow-brown to yellow-orange colour. Metallic to ashy reflectance. Hardness 5 to 5.5. Very common as alteration product in certain soils and sediments. Remains stable in recent soils of the temperate and humid climate zones, but  can be transformed into fine-grained Haematite with time. Identified in 1806 as a new mineral named in honour of the German poet Johann Wolfgang von Goethe, also a great collector of minerals.

A macroscopic sample of a crystalline mineral will generally consist of multiple conjoined crystals of varying shapes and sizes. Each of these crystals, within which the atoms are arranged on a single regular lattice, is termed grain