Structure and Composition of Seashells: Calcium Carbonate and Proteins


Seashells are fascinating structures that are commonly found on beaches and in marine environments. They are the protective outer coverings of various marine organisms, such as mollusks and crustaceans. The structure and composition of seashells play a vital role in providing protection, support, and defense for these organisms. In this article, we will explore the key components of seashells, focusing on calcium carbonate and proteins.

Calcium Carbonate

Calcium carbonate is the primary component of seashells, making up a significant portion of their structure. It is a crystalline compound composed of calcium, carbon, and oxygen atoms. The calcium carbonate in seashells exists in the form of the mineral aragonite or calcite. These minerals have distinct crystal structures, which can vary depending on the species of the organism that produces the seashell.

1. Aragonite

Aragonite is a less stable form of calcium carbonate compared to calcite. Many mollusks, including certain types of shells like those of abalone and conch, are composed predominantly of aragonite. Aragonite provides strength and durability to seashells, allowing them to withstand mechanical stress and protect the organisms inside.

2. Calcite

Calcite is a more stable form of calcium carbonate and is found in the shells of various marine organisms, such as clams, snails, and oysters. Calcite crystals are arranged in a lattice-like structure, making the shells resilient and resistant to dissolution in water. The calcite composition in seashells can vary, leading to different shell textures and appearances.


In addition to calcium carbonate, seashells also contain proteins that contribute to their structure and properties. These proteins play a crucial role in the formation, growth, and maintenance of seashells. They are involved in the regulation of calcium carbonate deposition and the control of crystal growth.

1. Matrix Proteins

Matrix proteins are a group of specialized proteins found in seashells. They act as organic templates and play a significant role in the nucleation and growth of calcium carbonate crystals. Matrix proteins help control the size, shape, and orientation of the crystals, influencing the overall structure and strength of the seashell. They also contribute to the flexibility and resilience of the shell, allowing it to withstand external pressures.

2. Glycoproteins

Glycoproteins are proteins that have attached carbohydrate molecules. They are abundant in seashells and are involved in various functions. One crucial role of glycoproteins is adhesive properties. They help bind the calcium carbonate crystals together, enhancing the structural integrity of the seashell. Glycoproteins also contribute to defense mechanisms by acting as anti-fouling agents, preventing the attachment of organisms, such as algae or barnacles, to the shell surface.


Seashells are complex structures with a unique composition and organization. The primary components of seashells are calcium carbonate and proteins. Calcium carbonate, in the form of aragonite or calcite, provides strength and durability to the shells. Proteins, including matrix proteins and glycoproteins, play essential roles in the formation, growth, and maintenance of seashells. They regulate the deposition of calcium carbonate and contribute to the overall structure, strength, and defense mechanisms of seashells. Understanding the structure and composition of seashells enhances our appreciation for the intricate adaptations of marine organisms and their ability to create these remarkable protective coverings.