Common Minerals in Biomineralization

There are common minerals that aid in biomineralization. Biomineralization is simply the process of how living organisms produce minerals. So this includes your skeleton, your pet’s skeleton, crab’s hard exterior, and all the shelly creatures! We will include some basic chemical formulas and what organisms make their hard parts out of which mineral!

Calcium Carbonate

Clear calcite crystals growing on light pink dolomite rock. Scale bar is 5 cm.

Calcite has a chemical formula of CaCO3; this means that there are calcium atoms within the crystals. The CO3 is equal to a carbonate ion, making calcite a form of calcium carbonate. This is the same carbonate that can make your soda or water bubbly! Calcite is the principal component in limestone rocks. When you put an acid on the limestone or similar carbonate rocks, they fizz. This is the acid reacting with the basic CaCO3 and forming a gas! This reaction is the same one that happens when you combine baking soda and vinegar – the common ingredients in a homemade volcano experiment.

Organisms with calcitic hard parts include: articulate brachiopods, echinoderms, oysters (a type of mollusk), trilobites, stromatoporoids, rugose and tabulate corals (extinct), and coralline algae.

Aragonite crystals.

Other mollusks, like most clams, snails, and cephalopods have shells composed of calcium carbonate, but a different form known as aragonite. Modern corals also have an aragonitic skeleton.

Aragonite has the same chemical formula as calcite (CaCO3), but the arrangement of atoms is different. This different arrangement results in less stable bonds within the crystal structure. Calcite and aragonite are polymorphs, different shapes of the same mineral.

Silica

Silica in the form of quartz minerals.

Silica (SiO2 or silicon dioxide) is a less common mineral than calcium carbonate used to build skeletons. Although silica is less common in biomineralization it’s one of the most common minerals found in Earth’s crust.

radiolarian
A radiolarian.

Organisms with siliceous hard parts include: radiolarians, diatoms, and hexactinillids (glass sponges). Diatoms and radiolarians are both types of plankton, this means they are very tiny animals that are producers in the food chain. Both are also considered to be microfossils (small fossils) and are studied by a specific subset of paleontologists. That includes paleoclimatologists like Adriane!

Phosphate

mammoth_tooth2
This Pleistocene mammoth tooth is made from apatite, the same mineral that makes up your teeth! Scale bar is 5 cm.

Apatite (Ca5(PO4)3(F,Cl,OH)) and related minerals are important for building skeletons, including yours! Phosporous (PO4) is the important compound in phosphate, the other elements that are separated by commas – Flourine, Chlorine, and Hydroxyl – are minor amounts.

Organisms with phosphatic hard parts include: Inarticulate brachiopods, bones and teeth of vertebrates (animals with backbones) and their close relatives (that may not always have a backbone but they still need to eat, nom).

Organic material

Resistant (or durable) organic material can be used to construct hard parts as well. This can include cellulose of plants and chitin. Chitin is usually a combination of proteins, polysaccharides (complex sugars), and occasionally some CaCO3. Essentially, organic material is made up of complex molecules with lots of carbon (C). Chitin, common mineralized hard parts of arthropods (crabs, lobsters, etc.), creates the hard exoskeleton that is shed as the animals molt.

horseshoe_crab_telson
The telson, or tail, of a horseshoe crab. Horseshoe crabs make their skeletons (called a carapace) out of cuticle, or chitin.

Common organisms with organic material in their hard parts include: Part of a horse shoe crab, called a cuticle, plant material and wood, and demosponges, a type of sponge that have spongin an organic protein as their skeletal material.

There are a variety of other types of organic matter that can be fossilized but less commonly than the carapaces of arthropods. Things such as keratin, which makes up your finger nails (strange, I know), also makes up the horns and hair of many animals through time. This does not often preserve well but it’s really awesome when you come across one in a museum collection. Also, we can’t forget feathers and scales, which don’t often preserve well but every so often can be found!

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