Apart from the crystal system, crystals are also found in groups. There are three main crystal groups; (i) Crystal Aggregated, (ii) Parallel Growth, and (iii) Twin Crystals.
(1). Crystal Aggregates:
The groups of associated crystals are found as ”crystal aggregates”. If the crystals forming the aggregate are made of one mineral only, the aggregate is said to be ”homogenous” and if different minerals are found in the crystal aggregate, it is known as ”heterogenous”. A number of crystals grown together so that each crystal in the group is large enough to be seen by the unaided eye and each crystal is more or less perfect. In gemmology, it differs from a crystalline aggregate, as a homogenous gem stone can be cut only from an individual crystal of a crystal aggregate.
(2). Parallel Growths:
When two or more crystals are grown in such a way that the crystallographic axes of one individual are parallel to the crystallographic axes of the other individual is known as Parallel Growth.
(3). Twin Crystals:
Twin Crystals show two separate portions joined at a common crystallographic plane. Geneculate twin of Rutile is a good example of twin crystals.
- Introduction to Crystallography
- Unit Cells of the Crystal Lattice
- Crystallographic Axes
- Interfacial Angle of Crystals
- Parameters of Crystal faces
- Crystallographic Notation
- Forms of Crystal faces
- Symmetry Elements of Crystals
- Six Types of Crystal Systems
- Cubic/ Isometric Crystal System
- Tetragonal Crystal System
- Hexagonal Crystal System
- Orthorhombic Crystal System
- Monoclinic Crystal System
- Triclinic Crystal System