Types of Stone

Where is breccia found?

Breccia is located wherever fragments of broken rocks or minerals accumulate, such as stream deposits and outcrop bases. The fragments are joined together by small rock particles or cement, which creates the breccia rock.Breccia is a type of clastic sedimentary rock that is comprised of angular fragments. These fragments are typically around 2 millimeters or larger. Breccia can be formed by many types of rocks and minerals, such as sandstone breccia, basalt breccia and limestone breccia. When fragments of different rocks join together, they form what is known as polymict breccia. The type formed in a specific location will depend on the rock fragments found in the area, as well as the climate.

How are conglomerate rocks formed? Conglomerate rocks are formed by the sedimentary rock process, which is: erosion, transport, deposition and cementation. Two characteristic properties of conglomerate rock are that the sedimentary particles, or clasts, are greater than 2 millimeters in size, and the clasts are rounded in appearance. Sedimentary rocks with angular clasts are distinguished from conglomerates and are called breccias.Conglomerates, like other sedimentary rocks, are formed from the detritus of source rocks, which results from weathering and erosion. As the pieces of source rock fall away, they are transported to other locations where they are deposited in layers. In the case of conglomerates, the transport by water causes the clasts to assume their rounded shape. As the sedimentary layers pile up in the stage of the formation process called deposition, pressure compacts the lower layers.The final stage of the process is cementation. This refers to the development of new minerals between the layered and compacted sedimentary particles. These new mineral growths bind the particles together. The process is helped along by water entering through the pores in the sedimentary layers, and depositing minerals such as calcium carbonate or silica, between the particles. The water-borne precipitates act like cement and also decrease the porosity, or the degree of open space, between the sedimentary particles until new hardened rock is formed.

How is sandstone formed?

Sandstone forms over the course of centuries, as deposits of sand accumulate in rivers, lakes or on the ocean floor, and the sand blends with calcite or quarts and then undergoes compression. After enough time goes by, the pressure pushes all of these elements together to create sandstone. Because not all sand is identical but instead comes in a variety of colors and grain textures, each formation has a unique appearance.One of the oldest cities in the world is Petra, an outpost in the desert of Jordan that is more than 2000 years of age. A lot of the structures there were carved out of sandstone in the area. Instead of containing a uniform appearance, though, the weavings of color make the buildings look like they are made of marble cake or marble rye bread.Some archaeologists have studied the formation of sandstone to determine how different layers of color ended up in the same sandstone. The most common theory is that a mixture of various sand types split into layers as the sand accumulated centuries or even millions of years ago. A similar process takes place in avalanches as the chaos of movement ensures that no two layers contain the same type of material.

How is siltstone formed?

Wind and rain erode rock to begin the formation of siltstone. The rock particles break down further as they travel with the water and then settle to the bottom of the water when it slows. Layers of silt accumulate, creating heat and pressure that cement the silt together into rock.Siltstone is a type of sedimentary rock formed from fine rock particles. Coarser rock particles are classified as sand or gravel and form sandstone, breccia or conglomerate rock as they are cemented together by heat and pressure. Very fine rock particles form a type of sedimentary rock known as shale or mudstone.As the particles of eroded rock travel with water, the edges of the rock are worn by the water into a rounded shape. Once these rounded particles are cemented together, other particles often occupy the abundance of space between the particles of silt. Calcite and quartz are two minerals that often fill the space between particles of silt. Oil and gas sometimes occupy this space, creating a reservoir that the petroleum industry can mine. Many oil and gas reservoirs are found near the mouths of large rivers, though some reservoirs are located inland where ancient rivers once existed.

How is shale formed?

Shale forms from the pressure of layers of sediment compressing bits of silt that settle into the clay on the bottom of bodies of water. The compressed clay and silt become shale over time. Shale is a sedimentary rock.Shale starts with bits of rock that erode off of larger rocks from contact with moving water and the weather. Very fine particles of feldspar, quartz, mica, pyrite and other minerals settle to the bottom of still bodies of water, such as swamplands, deep parts of the ocean and deep, still lakes. The fine rock particles mix with decaying organic matter into a mud. Because weathering is a continual process, new layers are always building up. The top layers press on the bottom layers with more and more pressure. When enough pressure builds up, the bottom layers become rock through a process called lithification. Lithification causes the thin layers that are characteristic of shale.Shale is a soft rock that breaks easily. The color varies depending on the exact minerals that formed the shale. Red, green and black are some color variations. Geologists classify shale as a claystone due to the small size of the particles that form the rock. Shale is a common rock that makes up much of Earth's crust.

What is rock salt made of?

Rock salt is made of a 1:1 ratio of sodium to chlorine. Rock salt's chemical formula is NaCl, which means that one molecule of rock salt is composed of one atom of sodium (Na) and one atom of chlorine (Cl).Rock salt is the common name for the mineral "halite." It is also known by its chemical name, sodium chloride, and is what is most commonly referred to as "table salt." In its solid form, each ion is surrounded by six other ions of the opposite charge. This is because rock salt is an ionic compound.

How is chert formed?

Chert is most often created when microcrystals of silicon dioxide are formed within soft sediments that over time will turn into chalk or limestone. When large amounts of silicon dioxide microcrystals are present in the sediment, they start to clump together and can eventually form whole layers of chert within a limestone deposit.

Chert is a sedimentary rock that is comprised of silicon dioxide. It is usually found as big layers tucked into chalk or limestone. Because of chert's structure, when it is broken, it often breaks into pieces with extremely sharp edges. Early humans noticed this quality and used this type of rock to create cutting tools and weapons. Chert is also often referred to as "flint."

When microcrystals start to clump together within specific sediment deposits, they will eventually lead to the formation of chert. These deposits are under a ton of pressure and, over time, will compress into either limestone or chalk. Silicon dioxide crystals form within the sediment and get transported by groundwater. The crystals start to pack together and create a layer within the sediment, which eventually turns into a layer of chert mixed into the many layers of chalk or limestone. When the silicone dioxide does not form layers, chert is instead formed as irregularly shaped nodules within the limestone or chalk.

How is iron oxide formed?

Iron oxide, commonly known as rust, forms as iron corrodes in an oxygen environment. Iron is especially eager to bond with oxygen, which is why pure iron is rare on the earth's surface. Corrosion requires the presence of an anode that gives up electrons, a cathode that accepts electrons, and an electrolyte that facilitates the flow of electrons between them.In the formation of iron oxide, iron is the anode. As a metal, iron usually permits the flow of electrons through it with little resistance. Paradoxically, this also makes iron an ideal cathode as electrons flow from one section of the metal to another through the electrolyte.The electrolyte that drives the oxidation is usually water. A drop of rain picks up carbon from the atmosphere as it falls, thereby transforming into weak carbonic acid. This acid in contact with the anode surface strips electrons from the iron surface and transmits them to the cathode. The energy this process imparts to the electrolyte breaks the bonds between hydrogen and oxygen in the water.The oxygen atoms displaced by the electrical flow through the electrolyte are taken up by the water and bond with the free oxygen. The molecules of iron oxide are much larger than those of the pure iron that formed it, so the thin oxide layer that forms on the iron surface sloughs off easily. This exposes a fresh surface to the carbonic acid and allows the process to continue.

How is limestone made?

Limestone can be formed as a result of evaporation, as is the case for stalactites and stalagmites in caves, or through the accumulation of calcium carbonate in marine environments. Limestone is either a biological or a chemical sedimentary rock, depending on its method of formation.Limestone formations created through evaporation are chemical sedimentary rocks, also known as travertine. They are formed when droplets containing calcium carbonate leak through cave ceilings and evaporate. As each evaporated droplet leaves behind a small amount of calcium carbonate, a stalactite forms. If droplets fall to the floor and then evaporate, a stalagmite extends upward as the calcium carbonate starts to pile up. Many caves are filled with these characteristic limestone teeth.Biological sedimentary limestone forms most often in warm, shallow marine waters in areas between 30 degrees latitude north and 30 degrees latitude south. This type of limestone is formed as marine organisms with calcium carbonate shells and skeletons die and accumulate layer by layer. Eventually, with extensive pressure and time, that calcium carbonate sediment hardens into limestone. These types of rocks often have fossils present in them. A less common method of limestone formation is through the direct accretion of calcium carbonate from either salt or fresh water.

How is dolostone formed?

According to About.com, dolostone refers to rock that is composed primarily of the mineral dolomite, which forms when calcite limestone is altered underground. This chemical change, called dolomitization, results in a reduced volume and recrystalization of the stone, making it more porous. This process is not fully understood by sedimentary geologists.The Kentucky Geological Survey describes dolostone as often having a "slightly sugary (saccharoidal) texture" and a tendency to turn to a buff or brown color as it weathers due to iron carbonate in the stone. It is harder and heavier than limestone and slower to bubble when exposed to dilute hydrochloric acid. Dolostone is commonly used for road aggregate, as agricultural limestone, in the making of rock wool, in the manufacture of magnesium and dolomite refractories, and as a component of natural cement. It is also used as a building material and as ornamental stone. Dolostone is important to the petroleum industry because of its natural porosity, which allows oil in the ground to travel more freely and form deposits, according to About.com.

How flint is formed?

Organisms such as sponges (on the macro scale) and radiolaria/diatoms (on the micro scale) use silica from sea water to manufacture the biogenic opal which forms their skeletons. When the organisms die and the organic parts decay the microscopic silica is scattered on the sea bed and becomes incorporated in the accumulating sediment.At depths of 1 to 5m within this sediment, the biogenic opal breaks down, enriching the water between the sediment particles (sediment pore water) with silica.At sediment depths of less than 10m, there is an oxic-anoxic boundary where hydrogen sulphide rising from the decomposing organic material within the sediment diffuses upwards meets oxygen diffusing downwards from the water column above. At this interface, the hydrogen sulphide is oxidised to sulphate with hydrogen ions as a by-product. The hydrogen ions lower the local pH, dissolving the chalk and thereby increasing the concentration of carbonate ions. These act as a seeding agent for the precipitation of silica.Silica precipitates by the molecule-by-molecule replacement of chalk. The silica is initially in the form of crystalline opal but gradually transforms to quartz (flint) during later burial and with time.The chalk sea bed is deeply burrowed by many different organisms, such as shells, echinoids and worms etc. Some of these burrows are quite deep or branching, or have open living spaces. The burrows fill with sediment after the organism has died, this is slightly different material from the sediment around it. These filled burrows act as preferential pathways (conduits) for the chemical reactions to occur. Flint formed within these old burrows often has a nodular shape which reflects the whole, or part of, overgrown remnants of such burrow systems.There are two possible explanations for why flint forms in bands or layers. Firstly because chalk sedimentation occurs in cycles and secondly because the process above exhausts the silica within a given depth of sediment and flint formation can only recommence when there is enough silica to start the process again.