Aragonite

Definition

Aragonite is a polymorph of calcium carbonate (CaCO3), a naturally occurring mineral that is an important component of many sedimentary rocks and marine organisms. It is closely related to the more common polymorph of calcium carbonate, calcite, and plays a significant role in the context of the occurrence, preparation, and properties of carbonates.

5 Must Know Facts For Your Next Test

1. Aragonite is a metastable polymorph of calcium carbonate, meaning it is less stable than calcite under standard conditions.
2. Aragonite is commonly found in marine environments, where it is a major component of the shells and skeletons of many organisms, such as corals, mollusks, and foraminifera.
3. Aragonite can be precipitated from seawater through inorganic processes, as well as through the biomineralization activities of marine organisms.
4. The formation of aragonite is influenced by factors such as temperature, pH, and the presence of specific ions in the surrounding environment.
5. Aragonite can undergo a phase transformation to calcite, which is the more stable polymorph of calcium carbonate, under certain conditions such as increased temperature or pressure.

Review Questions

• Explain the role of aragonite in the occurrence of carbonates.
  • Aragonite is a significant component of many sedimentary rocks and marine environments. It is a major constituent of the shells and skeletons of various marine organisms, such as corals, mollusks, and foraminifera. These aragonite-based structures can accumulate over time to form large deposits of carbonate rocks, such as limestone and dolomite. Additionally, the precipitation of aragonite from seawater, both through inorganic and biologically-mediated processes, contributes to the overall occurrence and formation of carbonate minerals in the natural environment.
• Describe the preparation of aragonite and its relationship to the properties of carbonates.
  • Aragonite can be prepared through various methods, including the precipitation of calcium carbonate from aqueous solutions under specific conditions of temperature, pH, and the presence of certain ions. The preparation of aragonite is closely linked to the properties of carbonates, as the polymorph of calcium carbonate (either aragonite or calcite) can significantly influence the physical and chemical characteristics of the resulting material. For example, aragonite has a different crystal structure and density compared to calcite, which can affect the hardness, durability, and other properties of the carbonate-based materials.
• Analyze the factors that influence the formation and stability of aragonite, and how this relates to the properties of carbonates.
  • The formation and stability of aragonite are influenced by various environmental factors, such as temperature, pH, and the presence of specific ions in the surrounding medium. Aragonite is a metastable polymorph of calcium carbonate, meaning it is less stable than calcite under standard conditions. However, certain conditions, such as the presence of magnesium ions or lower temperatures, can favor the formation of aragonite over calcite. The stability and transformation of aragonite to calcite can also affect the properties of carbonate-based materials, as the different polymorphs have distinct crystal structures, densities, and other physical and chemical characteristics. Understanding the factors that influence the formation and stability of aragonite is crucial for predicting and controlling the properties of carbonate-based materials in various applications, such as the construction industry, environmental remediation, and the production of biomimetic materials.

Related terms

Calcite:

Calcite is another polymorph of calcium carbonate, which is more stable than aragonite under standard conditions.

Carbonate Minerals: Carbonate minerals are a class of minerals that contain the carbonate ion (CO3^2-) and a metal cation, such as calcium, magnesium, or iron.

Biomineralization: Biomineralization is the process by which living organisms produce minerals, such as aragonite, for structural or functional purposes.