Chemical sedimentary rocks form when sediments settle from a solution.
Chemical sedimentary rocks can form from biological or non-biological processes, separating them into biochemical and inorganic chemical categories.
Biological processes are important in the formation of some sedimentary rocks like limestone and chert.
Some examples of chemical sedimentary rocks include limestones, gypsum, halite, dolomites, chert and more, which are all detailed below.
Chemical Sedimentary Rocks Examples (Characteristics and Types)
Limestones are made up of fragments of marine organisms that once made calcite for their shells.
These limestones are typically found in tropical regions with coral reefs and other areas with bodies of water.
The areas typically have ecosystems that reproduce often and will have calcium and bicarbonate ions in the water.
If limestone is found on dry land, it can be assumed that the area was once a body of water.
Limestone is made of calcite and aragonite, crystalline forms of calcium carbonate.
It can come in a range of colors between white and gray, including yellows and beiges as well.
Oolitic limestones can be found in ocean shallows and are formed from concentrated calcite developed in the tidal zone.
Oolitic limestones can be gray or transparent and look like a tiny pearl.
Oolites are made of calcium carbonate and can have some phosphate, chert, or iron minerals.
They are sometimes called egg stones.
These rocks can be found near Birmingham, Alabama, at Red Mountain.
Bioclastic and Skeletal Limestone
Bioclastic and skeletal limestones are formed from shell fragments, fossils and skeletal debris.
They are typically light to medium gray and are typically made of crinoids and bryozoans.
The rock will show button-like and branch-like sections due to the various fossils.
Bioclastic limestone can be found in low-latitude waters in the tropics.
Chalk is a form of limestone, formed in the deep sea originally by the compression of plankton settled along the sea floor.
It is composed of fragments of calcite shells, foraminifera or coccolithophores.
Chalk is mostly calcite with a little bit of other minerals like clay and quartz.
Chalk can be most commonly found in western Europe, mainly around parts of France and the Dover Cliffs.
Chalk is used for a variety of things that are involved in everyday life.
Chalk is used for bricks, builders’ putty and blackboard chalk.
Coquina is formed by large pieces of broken shells cemented together weakly.
When shell fragments are well-cemented, they are then classified as biosparite, which is a fossiliferous limestone.
Coquina are typically tan in color.
Coquina is composed of the mineral calcite and some phosphate in the form of coral and seashells.
Coquina can be found on the coasts of North Carolina, Florida, Brazil, Mexico, Australia and the United Kingdom.
Dolostones are formed when magnesium replaces some calcium in calcite within carbonate muds and sands.
Dolostones have a high percentage of mineral dolomite.
The rock can be any shade of gray, sometimes tan or white.
Dolostones can be found in the midwest United States, Mexico, Ontario, Switzerland and Spain.
Chert is formed from silica shells of marine organisms, diatoms and radiolaria.
Diatoms are phytoplankton and radiolaria are protozoa, both microorganisms.
There are different chert varieties such as flint that can be formed.
Chert typically shows up in colors from gray to red, including grayish browns and is very fine-grained.
Most cherts are mostly silica with a little calcite, dolomite and hematite.
Chert can be found in hot spring deposits, alkaline lakes, and in banded iron.
Flint is a variety of chert, formed from silica and usually appears in chalk and marly limestone.
Flint is typically a higher quality than common chert.
It can be found in Colorado, Florida, Mississippi, New Jersey, Ohio, Rhode Island and other different states throughout the United States in wild spaces.
For centuries, flint has been used as knives, stone tools and as a firestarter.
They are even used in jewelry today.
Flint is typically dark gray, green or black. It can sometimes be white or brown as well. It looks waxy or glassy.
Banded iron forms in shallow seas around the world.
They can be an important source of iron and typically have bands of iron oxides and iron-poor chert.
The iron bands are composed of magnetite or hematite and are usually darker in color than the chert bands.
These banded iron formations can be found in the United States, India, South Africa, Ukraine, Brazil, and other countries.
One common place in the United States for banded iron is in Michigan.
Evaporites are formed by minerals that came down after seawater or salt lakes have evaporated.
These are typically crystalline in nature and are water soluble.
Halite, or sodium chloride, is what is used as table salt worldwide.
It is formed of isometric crystals.
Gypsum is widely mined and used as fertilizer and as an ingredient to make plaster, blackboards, sidewalk chalk and drywall.
Borates, potassium salts and magnesium salts are also evaporates.
Borates are usually trigonal or tetrahedral and are mostly boron.
Potassium salts are typically used to treat low potassium levels in the blood.
Evaporites are found in arid regions, those with high temperatures and rare precipitation.
Stalactite and Stalagmite
Stalactite and stalagmite are found in caves.
Stalactites are icicle shaped and are along the ceiling of a cave.
They are formed by minerals dripping from water through the cave ceiling.
They generally have pointed tips.
Stalagmites are built up from the cave or cavern floor and are broader than stalactites.
They also usually have rounded or flattened tips.
In some cases, the stalactite and stalagmite join at a midpoint and form a pillar.
Stalactites and stalagmites can be found in Mammoth Cave in Kentucky, Luray Caverns in Virginia, Meramex Caverns in Missouri, Jewel Cave in South Dakota, and in various other caves around the United States.
Chemical sedimentary rocks are important resources used by humans daily.
They are needed for energy production and are useful as ingredients in fertilizers, cement, and foods.