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Subsoil
Also known as the B horizon, the subsoil is the part of the soil below the topsoil (A horizon) and above the parent material (C horizon). The subsoil is the thickest part of the soil. It contains very little organic matter. Roots in the subsoil do not find nourishment, but only water. Some plants have hardly any roots in the subsoil.
Sulphides
A group of important ore minerals (for example, pyrite, galena and sphalerite) in which sulphur combines with one or more metals.
Sulphur
An element and a mineral that can occur on its own as bright yellow and amber crystals and
in combination with many metals, for example, as iron pyrites,
iron sulphide. The element can form crystals in more than one crystal system.
Most sulphur becomes deposited directly from volcanic gases and so commonly occurs in volcanic rocks (see: Igneous rock).
Superficial deposit
Any layer of material that has been laid down over solid rocks. It may be used to describe alluvium or loess. This material is often many metres thick. The term is not used to describe soils.
T
Talc
A common grey–brown mineral in metamorphic rocks. Another word for talc is soapstone. The word
talc comes from the Arabic talq, meaning ‘mica’.
 Sulphur – Sulphur often forms bright yellow crystals near volcanoes and geysers.
Tectonic plate
A large piece of the solid, brittle outer part of the Earth that moves over the surface of the Earth independently of other parts of the crust.
 Tectonic plate – Tectonic plates, or just ‘plates’, are most significant where they push together to form new mountains. These are places where metamorphic rocks are made. New volcanic materials rise to the surface from both colliding plates and where plates pull apart.
Texture, soil
The proportion of sand, silt and clay particles in a soil. If a soil has more sand than clay or silt,
it has a sandy texture. When clay dominates, a soil has a clayey texture; and when silt is the most common size of particles, the soil has a silty texture. Roughly equal proportions of all sizes of particle are called a loam.
Sandy-textured soils warm up quickly in spring and drain well
in winter but may be prone to
dry out in summer. Clay soils warm up slowly in spring and may waterlog in winter. If they dry out in summer, they may crack open.
New mountains form where plates collide.
Texture, soil
Plates pull apart Oceanic plate
Magma chambers
Continental plate
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