# Crystal Structure, Unit Cell, Crystal Systems, the Seven Crystal Systems (For CBSE, ICSE, IAS, NET, NRA 2022)

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## The Seven Crystal Systems

### Triclinic System

All three axes are inclined towards each other, and they are of the same length. Based on the three inclined angles the various forms of crystals are in the paired faces. Some of the standard Triclinic Systems include Labradorite, Amazonite, Kyanite, Rhodonite, Aventurine Feldspar, and Turquoise.

Triclinic System

### Monoclinic System

- It comprises of three axes where two are at right angles to each other, and the third axis is inclined.
- All three axes are of different length. Based on the inner structure monoclinic system includes Basal pinacoids and prisms with inclined end faces.
- Some of the examples include Diopside, Petalite, Kunzite, Gypsum, Hiddenite, Howlite, Vivianite and more.

Monoclinic System

### Orthorhombic System

- It comprises of three axes and is at right angles to each other. There are different lengths. Based on their Rhombic structure orthorhombic system includes various crystal shapes namely pyramids, double pyramids, rhombic pyramids, and pinacoids.
- Some of the common orthorhombic crystals include Topaz, Tanzanite, Iolite, Zoisite, Danburite and more.

Orthorhombic System

### Trigonal System

- Angles and axis in a trigonal system are similar to Hexagonal Systems. At the base of a hexagonal system (cross-section of a prism) , there will be six sides. In the trigonal system (base cross-section) there will be three sides.
- Crystal shapes in a trigonal system include three-sided pyramids, Scalenohedral and Rhombohedra. Some of the typical examples include Ruby, Quartz, Calcite, Agate, Jasper, Tiger՚s Eyes and more.

Trigonal/Pyramidal System

### Hexagonal System

- It comprises of four axes. Among them, three axes are of the same length and are on one plane. They intersect each other at an angle of sixty degrees.
- The fourth axis intersects other axes at right angles. Crystal shapes of hexagonal systems include Double Pyramids, Double-Sided Pyramids, and Four-Sided Pyramids.
- Example: Beryl, Cancrinite, Apatite, Sugilite, etc.

Hexagonal System

### Tetragonal Systems

- It consists of three axes. The main axis varies in length; it can either be short or long. The two-axis lie in the same plane and are of the same length.
- Based on the rectangular inner structure the shapes of crystal in tetragonal include double and eight-sided pyramids, four-sided prism, trapezohedrons, and pyrite.

### Cubic System

All three angles intersect at right angles and are of equal length. Crystal shapes of a cubic system based on inner structure (square) include octahedron, cube, and Hexaciscoherdron. Example: Silver, Garnet, Gold, and Diamond.

Cubic System