Mantle Layers, Magma, Minerals and Rock Types

Asthenosphere and Upper Mantle

Asthenosphere is the layer beneath the lithosphere; it is less rigid and part of the upper mantle, which extends from about 100 to 670 km.

Mesosphere and D'' Layer

The mesosphere is the lower mantle, which ranges from about 670 km down toward the core. The lower boundary of the mesosphere is the D'' (D double-prime) layer, a zone roughly 0 to 200 km thick above the core-mantle boundary.

Mantle Convection and Plate Motion

The engine of plate tectonics is thermal convection in the mantle, which drives and explains the movement of tectonic plates.

Thermal plumes originate in the D'' layer due to density and temperature differences within the mantle. They are a source of hot material and influence the planet's internal heat loss.

Hotspots and Surface Heat Flow

Hotspots are areas of the surface that record high heat flow and where volcanic activity occurs.

Materials: Amorphous and Crystalline

Material — Amorphous: Chemical elements or compounds are found arranged in random order without periodicity. Examples: volcanic glass, opal, limonite, obsidian.

Crystalline matter: Constituents are regularly ordered in space, held together by chemical bonds, forming an internal crystalline structure.

Crystals and Minerals

A crystal is a solid, organic or inorganic, with an orderly structure and a defined chemical composition; it may be of natural or synthetic origin. Crystals form by solidification, crystallization, sublimation, recrystallization and mineralogical adjustment.

Mineral is a solid substance, an element or chemical compound whose composition varies within defined limits; it is inorganic, of natural origin, and has a defined crystal structure.

Polymorphs and Isomorphism

Mineral polymorphs are minerals with the same chemical composition but different internal crystal structures.

Ore minerals can be isomorphic: they share the same crystalline structure but differ in chemical composition.

Environments and Rock Formation

Environments are areas where Earth's geological processes occur and where minerals and rocks form. Each environment has different pressure and temperature conditions: igneous, metamorphic and sedimentary.

Rocks are aggregates of minerals. The minerals are joined in a way that preserves the properties of each; rocks are heterogeneous mixtures of substances.

Magma: Composition and States

Magma is molten rock material. The rocks from which it is generated are composed of silicates; magma is a silicate melt that can contain solid crystals and gaseous components.

Magma Types and Viscosity

Acidic magmas typically solidify at lower temperatures (~900–1200 °C), whereas basic magmas are hotter (around 1200 °C). Acidic magmas are more viscous than basic magmas. Basic magmas are more fluid; their silicates commonly include nesosilicates.

Magmatic Rocks: Plutonic, Volcanic and Filonianes

Magmatic rocks are formed through the solidification of magma.

Plutonic (intrusive) rocks form from magma that cools slowly away from the surface of the Earth; examples: granite, syenite, gabbro, peridotite.

Volcanic (extrusive) rocks are produced by rapid cooling, creating pyroclasts and lavas; examples: rhyolite, andesite, basalt.

Filonianes (vein or dike intrusions) are solidifications of magma within fractures; they include pegmatites.