Rock
Rocks are generally classified according to several characteristics such as mineral and chemical composition, the texture of the constituent particles, and permeability. The criteria used to distinguish between different types of rocks depends, however, on the processes that formed them. These indicators separate rocks into three types: igneous, sedimentary, and metamorphic. They are further classified according to particle size. The transformation of one rock type to another is described by the geological model called the rock cycle.
The three classes of rocks—the igneous, the sedimentary and the metamorphic—are subdivided into many groups. Igneous rock (derived from the Latin word igneus meaning of fire, from ignis meaning fire) forms through the cooling and solidification of magma or lava. Sedimentary rocks are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle and accumulate or for minerals to precipitate from a solution. Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock is subjected to heat and pressure.
The three classes of rocks—the igneous, the sedimentary and the metamorphic—are subdivided into many groups. Igneous rock (derived from the Latin word igneus meaning of fire, from ignis meaning fire) forms through the cooling and solidification of magma or lava. Sedimentary rocks are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle and accumulate or for minerals to precipitate from a solution. Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock is subjected to heat and pressure.
Pebbles
A pebble is a clast of rock with a particle size of 4 to 64
millimetres based on the Krumbein phi scale of sedimentology. Pebbles are generally considered to be larger than granules (2 to 4 millimetres diameter) and smaller than cobbles (64 to 256 millimetres diameter).
A rock made predominantly of pebbles is termed a conglomerate. Pebble tools are among the earliest known man-made artifacts, dating from the Palaeolithic period of human history.
A beach composed chiefly of surface pebbles is commonly termed a shingle beach. This type of beach has armoring characteristics with respect to wave erosion, as well as ecological niches which can provide habitat for animals and plants.
Pebbles come in various colors and textures, and can have streaks of quartz and different colored sedimentary rock. Pebbles are mostly smooth but, dependent on how frequently they come in contact with the sea, they can have marks of contact with other rocks or other pebbles. Pebbles left above the high water mark may have growths of organisms such as lichen on them, signifying the lack of contact with sea water.
Pebbles can also be found inland where ancient seas used to cover the land, when the seas retreat the rocks become landlocked. They can also be found in ponds. Pebbles can also form in rivers, and travel into estuaries where the smoothing continues in the sea.
millimetres based on the Krumbein phi scale of sedimentology. Pebbles are generally considered to be larger than granules (2 to 4 millimetres diameter) and smaller than cobbles (64 to 256 millimetres diameter).
A rock made predominantly of pebbles is termed a conglomerate. Pebble tools are among the earliest known man-made artifacts, dating from the Palaeolithic period of human history.
A beach composed chiefly of surface pebbles is commonly termed a shingle beach. This type of beach has armoring characteristics with respect to wave erosion, as well as ecological niches which can provide habitat for animals and plants.
Pebbles come in various colors and textures, and can have streaks of quartz and different colored sedimentary rock. Pebbles are mostly smooth but, dependent on how frequently they come in contact with the sea, they can have marks of contact with other rocks or other pebbles. Pebbles left above the high water mark may have growths of organisms such as lichen on them, signifying the lack of contact with sea water.
Pebbles can also be found inland where ancient seas used to cover the land, when the seas retreat the rocks become landlocked. They can also be found in ponds. Pebbles can also form in rivers, and travel into estuaries where the smoothing continues in the sea.