Définition : A group of hydrous aluminium phyllosilicate (phyllosilicates being a subgroup of silicate minerals) minerals (see clay minerals), that are typically less than 2micrometres in diameter. Clay consists of a variety of phyllosilicate minerals rich in silicon and aluminium oxides and hydroxides which include variable amounts of structural water.
Définition : Red clay, also known as pelagic clay, accumulates in the deepest and most remote areas of the ocean. Containing less than 30% biogenic material, its composition is a varied mix of very fine quartz and clay minerals, authigenic deposits precipitated directly from seawater, and micrometeorites. Though called "red" because it sometimes takes the color of oxidized iron minerals, it is usually brownish in color. Its ultimate origin is uncertain, but red clay seems to be mostly derived from distant rivers, and windblown dust. Covering 38% of the ocean floor, it accumulates more slowly than any other sediment type, at only 0.1-0.5 cm / 1000 yr.
Définition : A landform that extends above the surrounding terrain in a limited area. A mountain is generally steeper than a hill, but there is no universally accepted standard definition for the height of a mountain or a hill although a mountain usually has an identifiable summit and a local relief of more than 300m.
