What's the link between sea shells and toothpaste?
Sand occurs naturally, and is made up of very finely divided rock and mineral particles. The term sand refers to the size of these particles, not their composition.
These bits of pulverised and weathered rock and minerals and fragments of shelled creatures are washed up by the ocean and collect to form beaches. Because different rocks and minerals are formed from different things they do not all last; only the strongest survive, and that is way we have certain compositions in sand that are common.
The most common type of sand is made up of silicon dioxide, which has a chemical formula of SiO2, followed by the second most common component, calcium carbonate (CaCO3). Calcium carbonate is found all around us in nature, from snails' shells, to coral, to shellfish.
Sand is found all over the earth, in soil, on ocean floors, beaches, deserts, streams, and it is like a fingerprint and, with analysis, scientists can pinpoint its origins and location. In some volcanic regions, such as in Hawaii or the Canary Islands, the sand is often dark or black, due to the volcanic activity and the dark coloured volcanic rocks being broken down.
While common in sand, calcium carbonate is even more common in shells. They are usually washed up on the beach and have once belonged to a sea creature.
Sea shells are primarily the exo (outer) skeletons of mollusks such as sea snails, clams, oysters and many more.
Calcium carbonate is also found in many other places in nature: chalk, limestone, marble, Ireland's Burren region, hens' eggs and snails' shells. We use it in our personal care and food, as an antacid, as a calcium supplement in our diet, in toothpaste, and animal feeds.
The crystals of calcium carbonate can take on three forms: calcite, aragonite and vaterite. This means that while these crystals are all built of the same material, they differ in their structure.
The currently accepted understanding of how shell forms is from the bottom up. The initial layer is protein, and the rest is calcium carbonate. The protein is like the steel base and the calcium carbonate is like the concrete on top.
Therefore, the shell is continually being added to, as the calcium carbonate crystals grow. Ultimately there are three distinct layers and the inner layer is called the nacre (this is the pearly sheen you often see on shells used as jewellery).
Sea shells were often used traditionally as currency, particularly in areas such as the Indian Ocean and Pacific Islands. They have also found uses as bowls, or as jewellery.
Dr Sarah Hayes is Education and Outreach Officer, Synthesis and Solid State Pharmaceutical Centre (SSPC) at the University of Limerick