Triclinic System

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The branch of science which engages with the development, growth, internal structure, and external properties of crystals is Crystallography. It is the experimental scientific discipline of scrutinising the alignment of atoms in crystalline solids. The field's descriptive vocabulary includes terms like a crystal lattice, symmetry, crystal form, crystal family, and likewise. The distinctive terminology enables us to understand, analyse and empirically examine crystals. Let us start with the basics of the subject.

You can define the crystal lattice as the provision of an ordered internal structure to a mineral. The symmetry of a crystal is the periodic repetition of its structural features. By understanding the type of balance of a particular mineral, we can categorise it as one member of the seven crystal systems. 

The point symmetry operations include rotation, reflection, inversion, and rotoinversion. These operations can combine in different ways, and there exist thirty-two unique combinations of symmetry operations known as crystal classes. Each crystal class is a part of one of seven crystal systems according to the main symmetry operation it possesses. Each crystal of a specific crystal system will share a characteristic symmetry element with other system members. Furthermore, you can visually determine a mineral species' crystal system by examining a particularly well-formed crystal of the species. In Crystallography, there are seven primitive crystal systems – Isometric, tetragonal, orthorhombic, hexagonal, triclinic system, monoclinic, and rhombohedral or trigonal. 

The Triclinic Crystal System

The triclinic crystal system is the most disordered of all the crystal systems. The term 'triclinic' literally translates to 'three inclines'. The name is suggestive of the crystal system's unit cell that has three different inclining axes. Three axes of different lengths define the unit cell, all having different angles, and none of them is equal to 90 degrees. You can write the equation as a ≠ c and α ≠ β ≠ γ ≠ 90°. The crystals in the triclinic system possess a one-fold symmetry that is equal to no symmetry at all. 

Classes in the Triclinic Crystal System

The triclinic crystal system comprises two classes, namely, the pinacoidal class and the pedial class. The pinacoidal class has a centre of symmetry. It is also called 'triclinic normal'. On the other hand, the pedial class has no symmetry. It is alternatively known as 'triclinic hemihedral'. Now, you may ask what the centre of symmetry is. The answer is that a centre of symmetry is that central point inside a crystal that mirrors and inverts one side of the crystal to the other. Even you can create a crystal's centre of symmetry by rotating the crystal to 180 degrees and mirroring the image.

Triclinic Crystal Structure

The triclinic crystal structure refers to the ordered arrangement of atoms, ions, or molecules in a crystalline solid.  One can obtain the crystal structure by attaching atoms, groups of atoms or molecules. The structure occurs from the intrinsic nature of the constituent particles to create symmetric patterns. A unit cell is the building block of a crystal structure. You can define it as the repeated pattern of the atomic structure of the crystalline material. The unit cell explains the entire crystal structure and symmetry with the atom placements and its principal axes. A triclinic structure has the least symmetry among all the crystal systems. All the axes are inclined towards one another in the triclinic system, and they intersect at oblique angles, which is always less than 90 degrees. In case the axes cross at 90 degrees, we would be talking about the monoclinic crystal system. The structure and system determine the properties of a crystal.

Properties of Triclinic Crystals

You can characterise the triclinic crystals by unequal symmetry axes and inner structure organised in trapeziums. They are unique, beautiful and have fascinating properties. Mentioned below is a list of them.

The crystals of the triclinic system are harmonising and integrating. 

Crystal fracture refers to how a mineral breaks along irregular or nonlinear planes in its structure. Many minerals in the triclinic system have sub-conchoidal or an uneven fracture but brittle tenacity. This property implies that they are difficult to break, but their ability to resist deformation, that is, tenacity, is relatively low compared to other minerals. A few examples are albite, analcime, axinite and microcline.

Many of the crystals in the triclinic system have distinct to perfect cleavage - that is, a mineral's tendency to break along atomic planes of weakness—for example, kyanite, talc, turquoise, etc.

The Refractive Index of minerals in the triclinic crystal system is very different due to the variance in how tightly packed their lattice structures are. The one thing that they do have in common is that if you rotate the stone on a refractometer, the upper and lower values of the RI will move. This phenomenon happens because the stones are doubly refractive and are what we call biaxial. Biaxial stones have no two optical axes that are the same, and thus, light travels along the three axes at different speeds. The different speeds give a different RI value. The different values are reflected in the moving RI value on the refractometer as the stone turns.

Dispersion is the ability of a gemstone material to split light into the colours of the visible spectrum. Triclinic crystals like albite, anorthite, analcime, chabazite, kyanite, microcline and rhodonite have weak to no dispersion at all. Other minerals like axinite, babingtonite, pectolite, and turquoise have strong dispersion.

The Triclinic Prism

The triclinic prism is a complex structure. It is also known as the triclinic pinacoidal. The shape of the triclinic prism is three-dimensional and is similar to a cube. But, the design is skewed to one side, thereby making it oblique. A triclinic prism has six faces, twelve edges and eight vertices. 


The triclinic crystal system has complicated features and features. The minerals of this system are pretty unusual. Grasping the triclinic system in its entirety can be challenging. But, dedication, smart studying and Vedantu’s concept pages make the whole process much easier. The study of crystallography is an indispensable part of science and has tremendous significance in the practical and academic world.

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