Coquina rock is a type of sedimentary rock (specifically limestone), formed by the deposition and subsequent cementation of mineral or organic particles on the floor of oceans or other bodies of water at the Earth’s surface. In other words, the rock is formed by the accumulation of sediments.

� Rocks that are made from sediment are called sedimentary rock. Clastic sedimentary rocks are rocks that are made from weathered rock such as pebbles, sand, silt or clay….

For a sediment to be considered to be a coquina, the particles composing it should average 2 mm (0.079 in) or greater in size. Coquina can vary in hardness from poorly to moderately cemented.

Significant deposits of coquina are found along the coasts of Florida and North Carolina. They also occur along the coasts of Australia, Brazil, Mexico and the United Kingdom.

*Characteristics – fine-grained siltstone and shale, which are well stratified (layered) commonly, form in the central portion, whereas some well-sorted sandstone is also formed along the margins.

The park’s picturesque coquina outcroppings are some of the largest on the Atlantic Coast. A related building material is tabby, often called coastal concrete, which is basically manmade coquina. Tabby is composed of the lime from burned oyster shells mixed with sand, water, ash, and other shells.

The shells are made of minerals but they are not minerals. Coal is considered a rock but it is not made of minerals. These last three are called biogenic rocks.

Rocks formed by the evaporation of water are called evaporites – gypsum, anhydrite, halite (common salt). This evaporation may occur in either shallow basins on land or in the sea.

Typically, evaporite deposits occur in closed marine basins where evaporation exceeds inflow. The deposits often show a repeated sequence of minerals, indicating cyclic conditions with a mineralogy determined by solubility.

The most common minerals that are generally considered to be the most representative of marine evaporites are calcite, gypsum and anhydrite, halite, sylvite, carnallite, langbeinite, polyhalite, and kainite.

Iron-rich sedimentary rocks. Almost all sedimentary rocks are iron-bearing in the sense that mudrocks, sandstones, and carbonates typically have an iron content of several percent. The most important iron-bearing minerals in iron formations are hematite, magnetite, and greenalite.

Evaporite deposits (largely bedded halite, sylvite, gypsum, anhydrite, and various potash salts) form from the precipitation of solid mineral crystals from a concentrated solution of salt- or freshwater, in other words, from brine.

Sylvite, or sylvine, is potassium chloride (KCl) in natural mineral form. It forms crystals in the isometric system very similar to normal rock salt, halite (NaCl)….

potassium chloride

Sylvinite is a sedimentary rock made of a mechanical mixture of the minerals sylvite (KCl, or potassium chloride) and halite (NaCl, or sodium chloride).

Many limestones are biochemical; some may be chemical (inorganically precipitated). Evaporite rocks form when sea water or lake water dries up and precipitates gypsum (CaSO4·2H2O), halite (NaCl), or other minerals. Evaporites are chemical sedimentary rocks.

A typical shale seal has a permeability ≈ 10-1 to 10-5 md, with rare values as low as 10-8 md (Figure A). Bedded salt formations can contain a significant amount of insolubles (clay, anhydrite), which might be more permeable than the salt itself (Warren, 2017).

Gypsum is a chemical sedimentary rock. It forms when large bodies of water are rich in calcium and sulfate.

Crude gypsum is used as a fluxing agent, fertilizer, filler in paper and textiles, and retarder in portland cement. About three-fourths of the total production is calcined for use as plaster of paris and as building materials in plaster, Keene’s cement, board products, and tiles and blocks.