# What is the rarest crystal system?

The rarest crystal system is the trigonal or rhombohedral system. Only 5% of all known minerals belong to this system. The trigonal system is characterized by a threefold axis of symmetry, as well as a single fourfold axis perpendicular to it.

The other six crystal systems are:

• Cubic
• Tetragonal
• Orthorhombic
• Monoclinic
• Triclinic
• Hexagonal

The cubic system has the most symmetrical arrangement of atoms, with three fourfold axes of symmetry and four threefold axes. The tetragonal system has a fourfold axis of symmetry and two perpendicular twofold axes. The orthorhombic system has three mutually perpendicular twofold axes of symmetry. The monoclinic system has a single twofold axis of symmetry and one unique axis that is perpendicular to it. The triclinic system has no axes of symmetry. The hexagonal system has a sixfold axis of symmetry and three twofold axes.

Each crystal system has unique physical properties and energetics, allowing crystal practitioners to work with them for different purposes. The rareness of the trigonal system makes it particularly valuable for collectors and practitioners seeking to work with something truly unique.

## The Unique Properties of Crystal Systems

Crystals are fascinating structures that are formed by atoms, ions or molecules arranged in a particular pattern, in a regular and repeating way. A crystal’s shape, color, and other physical properties depend on the arrangement of atoms or molecules. The study of crystals, known as crystallography, is an important field of science that helps us to understand the structures of materials, their formation, and their properties.

There are seven crystal systems, each with unique properties that distinguish them from one another. The crystal systems are the building blocks of crystal structure classification, and they are determined based on the arrangement of atoms or molecules within a crystal. Each crystal system has its own set of symmetry operations, which describe how the crystal looks the same when it is viewed from different angles.

## What Determines the Rarity of a Crystal System?

The rarity of a crystal system is determined by the frequency at which it occurs in nature, as well as its usefulness in technology and industry. The rarest crystal systems are those that are less commonly found in nature and are more difficult to grow or synthesize in a laboratory setting.

While some of the rarest crystals systems may have unique and useful properties, they are often difficult to mass-produce, making them less common than other crystal structures. For this reason, many rare crystals are highly prized by collectors and used in specialized applications.

## Exploring the Rarest Crystal System

The rarest crystal system is the Triclinic system. Triclinic crystals are characterized by the absence of any bilateral symmetry, that is, there is no axis, plane, or center of symmetry in the crystal structure. This unique feature leads to some interesting optical properties, such as birefringence, which allows the crystal to split light into two different directions.

Triclinic crystals are found in a limited number of minerals, such as feldspar, a mineral commonly used in the production of ceramics and glass, and the gemstone turquoise. Because of their optical properties, triclinic crystals are also used in optical instruments such as polarizing microscopes.

## An Overview of the Seven Crystal Systems

1. The Trigonal Crystal System: Crystals in the trigonal system have a three-fold axis of symmetry, and are characterized by their triangular prisms, pyramids or dipyramids. Examples of minerals in this system include quartz and tourmaline.

2. The Tetragonal Crystal System: Crystals in the tetragonal system are characterized by their tetragonal prisms or dipyramids, and have a four-fold axis of symmetry. Examples of minerals in this system include zircon and titanite.

3. The Orthorhombic Crystal System: Crystals in the orthorhombic system are characterized by their orthorhombic prisms and dipyramids, and have three axes of symmetry that are perpendicular to each other. Sulfur and topaz are examples of minerals in the orthorhombic system.

4. The Monoclinic Crystal System: Crystals in the monoclinic system have one axis of symmetry that is not perpendicular to the other two, and are characterized by their monoclinic prisms and dipyramids. Gypsum and apatite are examples of minerals in this system.

5. The Triclinic Crystal System: As discussed earlier, the triclinic system has no bilateral symmetry and is characterized by its triclinic prisms, pinacoids, and pedions. Minerals such as feldspar and turquoise belong to this system.

6. The Cubic Crystal System: Crystals in the cubic system are characterized by their cubic form and have three axes of symmetry that are equal in length and perpendicular to each other. Examples of minerals in this system include diamond and pyrite.

7. The Hexagonal Crystal System: Crystals in the hexagonal system are characterized by their hexagonal prisms and pyramids, and have a six-fold axis of symmetry. Minerals such as beryl and calcite belong to this system.

In conclusion, crystal systems play a significant role in the classification of minerals and materials, and they help us understand the unique properties of different crystal structures. While the triclinic system may be the rarest of the seven, each system has its own distinct properties that make them valuable in their own way. As technology advances, there may be an increasing demand for these unique crystal structures, making them even more valuable in the future.