Rhombohedral

Definition

Rhombohedral refers to a type of crystal system characterized by three axes of equal length that intersect at oblique angles. This unique arrangement contributes to the symmetry and geometric properties of minerals, playing a significant role in the classification of crystalline structures and mineral chemistry, particularly in carbonate minerals, which often exhibit rhombohedral symmetry.

5 Must Know Facts For Your Next Test

1. The rhombohedral crystal system is one of the seven crystal systems in mineralogy, distinct from cubic and hexagonal systems.
2. Common examples of rhombohedral minerals include calcite and dolomite, both of which are carbonates known for their rhombohedral cleavage.
3. In rhombohedral crystals, the angles between the axes are not right angles, which distinguishes them from more symmetrical crystal systems.
4. Rhombohedral symmetry is important for understanding how minerals grow and interact with light, impacting their optical properties.
5. The structural arrangement in rhombohedral crystals allows for unique chemical bonding patterns, influencing the physical properties of minerals.

Review Questions

• How does the rhombohedral crystal system differ from other crystal systems in terms of symmetry and lattice structure?
  • The rhombohedral crystal system differs from other systems primarily through its unique lattice structure where three axes are equal in length but intersect at oblique angles rather than right angles. This arrangement leads to distinct geometric properties and symmetry, setting it apart from systems like cubic or tetragonal, which have more regular angles. The specific symmetry of rhombohedral crystals affects their cleavage patterns and overall mineral behavior.
• Discuss the role of rhombohedral symmetry in the classification and identification of carbonate minerals.
  • Rhombohedral symmetry plays a critical role in classifying carbonate minerals such as calcite and dolomite. The distinctive cleavage patterns associated with rhombohedral crystals aid in their identification under a microscope or through physical examination. This symmetry allows for a specific arrangement of atoms within the mineral structure, directly influencing their chemical properties and interactions with environmental factors.
• Evaluate the impact of rhombohedral crystal structures on the physical and optical properties of minerals, using examples.
  • Rhombohedral crystal structures significantly influence both the physical and optical properties of minerals. For instance, calcite exhibits strong birefringence due to its unique symmetry, leading to interesting light behavior when observed through polarizing filters. The cleavage characteristics associated with rhombohedral structures also affect how these minerals break and their usability in various applications, such as in construction materials or decorative stones. Analyzing these impacts helps to understand why certain minerals are favored for specific uses based on their structural properties.

Related terms

Crystal System: A category that classifies crystals based on their lattice parameters and symmetry, including systems like cubic, tetragonal, and hexagonal.

Lattice Parameters: The constants that describe the size and shape of a unit cell in a crystal structure, which are critical for determining the symmetry and properties of crystals.

Carbonate Minerals: A group of minerals that contain the carbonate ion ($$CO_3^{2-}$$), often exhibiting rhombohedral crystal habits and significant in geology and mineralogy.