The chemistry of crystals is very beautiful. It is the crystal structure by which we name the particular crystal, a crystal. Scientifically, there are 7 types of crystals structure and shapes divided into Lattices (shape). We will today focus on the lattice shape of crystals and their properties. Each crystal type is described by the relationship of lattice sides i.e. a, b, c and angles, α, β and γ. The structures of crystals can be defined as per their symmetry of the unit cells.

### Types of Crystals by Lattices (Shape)

Here are described under 7 different shapes of crystals:-

- Cubic
- Hexagonal
- Tetragonal
- Trigonal
- Orthorhombic
- Monoclinic
- Triclinic

**1- Cubic or Isometric:**

The cubic crystal structure has the loveliest and good symmetry. All angels are equal to 90° with equal length measurement on all sides. One will see octahedrons (eight faces) and dodecahedrons (10 faces).

**Axial Relationships:** a = b = c ** Interaxial Angles**: α = β = γ = 90°

**Unit Cell Geometry**:

**Examples of gems and minerals:** Diamond, Flourite, Garnets, Pyrite, Spinels

**2- Hexagonal:**

In this form, the crystal will have a cross-section with 6 sided prism or hexagon. The crystal structure can be seen as a prism with hexagons as the bases.

**Axial Relationships**: a = b ≠ c ** Interaxial Angles**: α = β = 90° and γ = 120°

**Unit Cell Geometry:**

**Examples of minerals and gemstones:** Beryl

**3- Tetragonal:**

One axis will be longer than the other. These crystals form double prisms and pyramids. It is almost similar to cubic. All angles will be equal 90° along with 2 sides same in length. Quite unique symmetry in the axis.

**Axial Relationships**: a = b ≠ c ** Interaxial Angles**: α = β = γ = 90°

**Unit Cell Geometry**:

**Examples of minerals and gemstones: **Zircon

**4- Trigonal:**

This crystal system will have a single 3 fold axis of rotations. Unlike 6 fold axes of the hexagonal structure.

**Axial Relationships:** a = b = c ** Interaxial Angles**: α = β = γ ≠ 90°

**Unit Cell Geometry:**

**Examples of minerals and gemstones:** Calcite, Corrundum, tourmaline, Quartz

**5- Orthorhombic:**

This crystal structure is similar to tetragonal except one difference of not being square in cross-section. They have rhombic prisms or dipyramids.

**Axial Relationships**: a ≠ b ≠ c **Interaxial Angles:** α = β = γ = 90°

**Unit Cell Geometry:**

**Examples of minerals and gemstones:** Chrysoberyl, Peridot, Topaz, Tanzanite,

**6- Monoclinic:**

This crystal system form double pyramids and prisms. They introduce a restriction on 2 of the angles. For example, α and γ must equal to 90° making the side symmetry.

**Axial Relationships:** a ≠ b ≠ c **Interaxial Angles:** α = β = γ ≠ 90°

**Unit Cell Geometry: **

**Examples of minerals and gemstones:** Feldesper,

**7- Triclinic:**

This crystal structure is not uniform or have side symmetrical form leading the crystals towards uneven shapes. The other name of triclinic is anorthic crystal structure. It has very low symmetry. There is almost no restriction on the angles or sides.

**Axial Relationships:** a ≠ b ≠ c **Interaxial Angles**: α ≠ β ≠ γ ≠ 90°

**Unit Cell Geometry**:

**Examples of minerals and gemstones:**Kynite, Axinite, Albite, Rhodonite, Chalcanthite