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Crystal Structure

Crystal Structure

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Crystal structure  is the unique arrangement of atoms or molecules in a periodic pattern contained within a unit cell. This implies that a crystal structure contains a set of atoms or molecules arranged in a certain way and a lattice kind of symmetry. Patterns are basically located on an array of points repeating periodically on three dimensions. This array of points is known as lattics. The points are imagined to be forming tiny boxes called unit cells, which fill up, the spaces of the lattice. The length and angle between the edges of the unit cell is known as lattice parameters.

Excuse the self indulgence with the image above but we felt it was more tasteful than a scientific diagram!

The symmetry of crystal structure plays a major role in determining the many properties of a crystal structure. The unit cell as earlier stated is a small box that contains one or more atoms arranged in a spatial pattern. These unit cells themselves are stacked in three dimensional space, and this furthermore describes the bulk arrangement in a crystal structure.

The atomic planes and vectors of a crystal structure can be determined by a value known as miller index notation, which is denoted by (l,m,n). The l,m, and n represents directional indices and are separated by an angle of 90 degrees, therefore, they are orthogonal; consequently the miller indices are the inverse of the intercept of the plane with the unit cell. In a crystal structure, the crystallographic directions are fictitious lines that link to the nodes while the crystallographic planes are fictitious planes that link the nodes together. As a result, some directions and planes have higher density than others. This higher density is the sole reason behind the behavioural attributes of a crystal structure.

There are some striking properties that crystal structures are known for, and some of the most notable ones includes, optical properties, this mainly involves the refractive index. The refractive index of a crystal structure is highly influenced by density of the planes and lines this therefore determines the refraction of light from different crystal structure whereby the higher the density the more the refractive index is shifted. Another notable property of a crystal structure that is affected by density of the planes and lines is the absorption and reactivity of the crystals absorption and chemical reaction occur near surface of atoms in a crystal structure and these properties are sensitive to node density. The other property affected by density in a crystal structure is the surface tension.

Crystal structures can encounter some deformities and which are referred to as crystal defect or impurities. These defects occur basically due to misplacement of an atom or a group of atoms in the unit cell thereby disrupting the periodic pattern of the structure.

Additional Resources

Crystal   Density   Dike

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