Rocks provide the sediment that creates the seabed, beaches and shoreline surrounding Long Island Sound. Rocks also provide a solid substrate for filter feeders, which are found along the seashore, to attach themselves to. According to the book, Rocks: Earth Science Discovering the Secrets of the Earth, rocks are comprised of a mixture of minerals. There are three types of rocks; igneous, sedimentary and metamorphic. Igneous rocks are formed as molten rock known as lava (at the surface) or magma (below the ground) solidifies. Sedimentary rocks are formed from the breakdown of pre-existing rocks and the broken grains are deposited in layers by the wind, water and/or glaciers. The layers will harden into sedimentary rock over time. Metamorphic rocks are found deep in the Earth's crust as heat, pressure or both transforms other types of rocks to form completely new rocks, such as marble, which is metamorphosed limestone, and minerals. such as diamonds.
Sedimentary rocks are formed from the fragments of other rocks and often contain distinct and visible layers or strata. The fragments of the rocks are carried by rivers, oceans or wind and deposited into beaches, deltas and sand dunes. There are three types of sedimentary rocks, clastic, chemical and organic rocks. Clastic rocks are made of smaller pieces of rocks, which are weathered from other rocks. Chemical rocks are deposited using some form of chemical action, such as precipitation of minerals from solution. Organic rocks are made of materials produced by living things, such as shells making up reef limestone or plants making up coal.
Sedimentary rocks form in lakes, rivers and shallow seas or basins close to the edge of land. The pattern in which the sedimentary rocks carried by the rivers are laid down changes based on the changing pattern of a flood or drought. As the sedimentary rocks are dependent on the materials the river delivers and deposits, their layers vary in texture and thickness. Most sedimentary rocks are formed under the sea or at the seafloor.
These rocks are valuable in providing a record of how they formed, the conditions, water depth and climate under which they formed, as well as the time when they were laid down, which can be determined from the fossils found within the strata or layers of the rock.
Igneous rocks begin as liquid or molten rock. They are the most uniform of all the rocks because the molten rock is constantly churning and mixing its ingredients. Igneous rocks make up the floor of all of the oceans and thus, cover about seventy percent of the surface of the earth. Igneous rocks can be categorized into two groups, extrusive or intrusive.
Extrusive or volcanic rocks are rocks that have reached the surface before they have cooled. Extrusive rocks include ash and lava. Molten rock or magma erupts from a volcano and will flow, cool and then turn into solid rock. Magma is a mixture of liquid and a few solid pieces. The liquid fraction of magma is a mixture of dissolved chemicals, some of which are gases. The rate at which the magma or lava cools determines the nature and size of the crystals that will form. If the magma/lava cools rapidly, the crystals will stop growing and will be small. If the magma/lava cools slowly, the crystals continue to grow and will be large, for example granite.
Intrusive rocks are rocks that have cooled while still inside of the earth's crust. Intrusive rocks cool more slowly because the rocks surrounding them act as insulation. Gases are not eliminated because these rocks will remain under pressure as they form. Crystals will grow in magma that is cooling very slowly, which happens deep in the earth. Some intrusive rocks are formed close to the surface, making sheets of rock forming between others called dikes or sills (East Rock, West Rock and Sleeping Giant are all examples of intrusive dikes/sills). The cooling of these types of rock sheets will be quick and the crystals will be smaller. The minerals that form during this slow cooling of rock depend in part on the temperature at which they melt. The crystals that grow first will usually be formed the best and have the most perfect of geometrical shapes.
Metamorphic rocks are rocks that were either sedimentary or igneous rocks. The most common feature of these rocks is that they consist entirely of crystals, however, they are not always interlocking and have a tendency to face the same direction. There are several different ways in which rocks can be changed, so there are many different types of metamorphic rocks. The type of metamorphic rock formed depends on the amount of heat, pressure, the original texture of the rock being changed as well as the minerals the rock is made of. As the amount of heat and pressure increases, the metamorphic rocks produced from a typical mud deposit will be shale, then slate, then, phyllite, schist and finally gneiss. Metamorphic rocks are commonly found in places in which mountains once formed.