Generally speaking, the diamond pictured above, also known as diamond, has the mineral name diamond. Its chemical composition is carbon, the only single element in the gemstone, which belongs to the equiaxed crystal system.

### (1) Seven basic modes

The crystal structure of diamonds is very complex, but there are three main types:

**(1) tetrahedron, (2) octahedron, (3) rhombic dodecahedron.**

And because diamonds are cubes, cubes have three equal-length axes that are perpendicular to each other, making it the most symmetrical system in a crystal. The cubic system of diamonds produces unique crystal patterns with unique "habits". These basic patterns are as follows:

1; A cube consists of six square faces, each of which is at right angles to each other, and the axes are also at right angles to each other. Industrial diamond crystals usually come in cubic crystal shapes.

2; The octahedron consists of eight equilateral triangular faces with the same length of the crystal axis from the center point to each face. Most gem-quality diamond crystals are of this shape.

3; The dodecahedron consists of twelve rhombic faces, and it is unusual for a diamond crystal to appear in this shape.

4; The tetrahedron, replaced by twenty-four isosceles triangles, becomes this shape. Gem-quality diamond crystals rarely have this morphology.

5; An equilateral quadrilateral consists of twenty-four faces of an equilateral quadrilateral. The eight faces of the octahedron are replaced by three equilateral polygons, which are not many gems.

6; The octahedron consists of 24 isosceles triangular faces and is a common variant of the octahedron. The eight faces of the octahedron are replaced by three equilateral triangles.

7; The octahedron is composed of twenty-four triangles, and each face of the octahedron is composed of six triangles.

### (2) Growth lines

In fact, the form of crystals does not appear in a simple basic form. Usually, two or more crystals are mixed together, but most crystals tend to be octahedral. There is a feature on the surface of a diamond that is very important to the cut, that is, the 'growth pattern', which can help us identify the authenticity of a diamond. Many older diamonds cannot exhibit the unique brilliance of diamonds because the cut patterns are too old and the angles and proportions are wrong. Therefore, the growth lines left on the unpolished surface become an important reference for identification. There are certain standards for growth lines. The growth lines on the octahedron become triangular grooves, and the three sides of the triangular grooves must be parallel to the sides of the octahedron. The growth lines on the rhombic dodecahedron are groove-shaped, and the grooves are parallel to the diagonals of the rhombic surface. The growth pattern on the cube becomes a square groove, and the four sides of the square groove must be parallel to the diagonal of the cube surface.

### (3) Double crystal

In addition to the above seven basic forms, diamond crystals also have a very important form, that is, "twin crystals". Twins are also important for cutters. There are many kinds, but only two or three are common. The octahedral-looking twin, which experts call Michael, is the most common of twins. Cutting, sawing, and polishing are very difficult due to the inconsistent lines of the twins. At the same time, the twin crystal is relatively flat, and it requires a lot of weight to cut and grind into a round diamond. Therefore, the twin crystal is undoubtedly a challenge to the cutter.