Crystal Systems
Introduction to Crystal Systems
Crystal systems are a way of classifying crystals based on their symmetry and lattice parameters. In crystallography, the study of crystal systems helps scientists understand the internal structure of crystals, which in turn influences their physical properties, such as optical behavior and mechanical strength.
There are seven primary crystal systems in crystallography: cubic, tetragonal, orthorhombic, hexagonal, trigonal, monoclinic, and triclinic. Each system is defined by specific symmetry elements and the lengths and angles of the axes that make up the crystal lattice.
This page provides an introduction to the various crystal systems, explaining their defining characteristics and how they relate to the formation and properties of different minerals and gemstones.
Cubic Crystal System
The cubic crystal system, also known as the isometric system, is one of the most symmetrical crystal systems. Crystals in this system have three axes of equal length that intersect at right angles. This high degree of symmetry gives cubic crystals their characteristic shapes, such as cubes and octahedrons.
Common minerals in the cubic system include diamond, garnet, and pyrite. The simplicity and symmetry of the cubic system make it a fascinating subject for study in crystallography and a favorite among collectors and jewelers.
Explore this section to learn more about the cubic crystal system, its defining features, and examples of minerals that crystallize in this system.
Tetragonal Crystal System
The tetragonal crystal system is characterized by two axes of equal length and a third axis that is either longer or shorter than the other two. This system has a lower symmetry than the cubic system but still maintains a high degree of regularity.
Tetragonal crystals often form prismatic or columnar shapes. Notable examples of tetragonal minerals include zircon and rutile. These minerals are prized for their distinct shapes and the unique optical properties that arise from their crystal structures.
In this section, you will explore the tetragonal crystal system, including its key characteristics, examples of tetragonal minerals, and the importance of this system in gemology and materials science.
Hexagonal Crystal System
The hexagonal crystal system is defined by four axes: three of equal length that intersect at 120-degree angles in a single plane, and a fourth axis that is perpendicular to this plane and of a different length. This system produces crystals with hexagonal or trigonal symmetry.
Minerals like quartz, beryl, and apatite crystallize in the hexagonal system. The hexagonal crystal system is known for producing some of the most visually striking crystals, such as the six-sided prisms of quartz.
This section offers an in-depth look at the hexagonal crystal system, discussing its symmetry, common minerals, and the role of this system in the formation of many popular gemstones.
Orthorhombic Crystal System
The orthorhombic crystal system has three axes of unequal length, all intersecting at right angles. This system has a moderate level of symmetry, with crystals typically forming prismatic or tabular shapes.
Common minerals in the orthorhombic system include topaz, olivine, and sulfur. These minerals often exhibit a variety of colors and forms, making them highly desirable in both scientific study and gemstone collection.
Explore this section to learn more about the orthorhombic crystal system, its distinctive features, and the minerals that crystallize in this system.
Trigonal Crystal System
The trigonal crystal system is a subdivision of the hexagonal system, characterized by threefold rotational symmetry. Crystals in this system have three axes of equal length intersecting at 120-degree angles, with a fourth axis that is different in length and perpendicular to the other three.
Trigonal crystals can have complex and varied forms, including rhombohedra and scalenohedra. Notable minerals in the trigonal system include calcite and tourmaline, which are known for their striking optical effects and diverse crystal shapes.
In this section, you will explore the trigonal crystal system, including its unique symmetry elements, common minerals, and the significance of this system in the study of crystallography.
Monoclinic Crystal System
The monoclinic crystal system is characterized by three axes of unequal length, with two axes intersecting at an angle other than 90 degrees, while the third axis remains perpendicular to the plane formed by the other two. This system has lower symmetry than the previous systems but is still capable of forming a wide variety of crystal shapes.
Common minerals in the monoclinic system include orthoclase, gypsum, and spodumene. These minerals often display unique forms and optical properties, making them important subjects of study in mineralogy and gemology.
Explore this section to learn more about the monoclinic crystal system, its defining characteristics, and the minerals that crystallize within this system.
Triclinic Crystal System
The triclinic crystal system has the least symmetry of all the crystal systems, with three axes of unequal length that intersect at angles other than 90 degrees. Crystals in this system often have irregular and less symmetrical shapes.
Despite its low symmetry, the triclinic system includes several important minerals, such as albite and kyanite. These minerals can exhibit complex and beautiful crystal forms, making them of great interest to both collectors and scientists.
In this section, you will explore the triclinic crystal system, including its symmetry elements, the types of minerals found in this system, and the challenges and rewards of studying triclinic crystals.