GeologyRocks

S Wave

A seismic body wave that has motion perpendicular to the direction of travel (i.e. like light waves). They cannot travel through liquids and are slower than P Waves.

Sandstone

A clastic rock composed of sand-sized grains, i.e. between 0.625 and 2mm. The term usually implies a quartz rich composition, although this is not strictly necessary.

Secondary Mineral

A mineral which has subsequently formed in-situ due to secondary processes, such as oxidation or weathering. A good example is the alteration of olivine to secondary chlorite and serpentine.

Seismology

The study of earthquakes and the structure of the earth via seismic waves. This covers whole earth structure (global seismology) and crustal structure (exploration seismology). Exploration seismology is used in commercial operations, such as oil exploration.

There are two types of seismic waves that travel through the interior of the Earth; P-waves and S-waves.

Sequence stratigraphy

Sequence stratigraphy is a branch of geology that attempts to link relative sea-level changes to sedimentary deposits. The essence of the method is mapping of strata based on identification of time lines, such as unconformities, maximum flooding surfaces and transgression surfaces. In doing so it places stratigraphy in chronostratigraphic framework.

Sexual Selection

Variation in reproductive success due to variation in the ability to acquire mates.

Silica Tetrahedra

All silicate minerals have a structure based on the silica tetrahedra, an arrangement of 1 silica atom and 4 oxygen atoms. The chemical formula for this is SiO₄.

Silicate

A mineral formed from silica and oxygen. The majority of rock forming minerals are silicates. Examples are quartz and pyroxene.

Silliminite

A polymorph whose other two minerals are kyanite and andalusite.

Silurian

A geological period; the third of the Paleozoic Era from 443 to 416Ma. The fossil record from this period includes a huge variety of marine fossils, land plants and early invertebrate land animals.

Epochs:

• Prídolí 418-416Ma
• Ludlow 422-418Ma
• Wenlock 428-422Ma
• Llandovery 443-428Ma