What comes to your mind when you think of crystals? Is it the dazzling diamond or the expensive crystal centerpiece? Well, for those who nodded their head up and down, here is a small surprise. Little did you know that crystals are as common a commodity as daily products, and are, knowingly or unknowingly, used in day-to-day life for umpteen purposes! Yes, those little solid minerals found in different sizes and structures are plenty in number. Salt, sugar, diamond, ruby, snowflake, gemstones and quartz are just a few crystals to name. The component ions, atoms and molecules are arranged in a particular structure to give the crystal a definite pattern. Arrangements of these building blocks can be either random or very different throughout the crystal. Depending upon the arrangement of the constituent particles, each crystal depicts a different shape, size, color, and physical and chemical properties. With numerous crystals on our list, crystals are classified according to their shape and properties. Read further to know the different kinds of crystals based on different categorizations.
Different Kinds Of Crystals
On the Basis of Shape
Cubic or Isometric
Crystals falling under this category are of the same length along all axes. Not necessarily four-sided (cubic), such crystals can also be eight-sided (octahedrons) and ten-sided (dodecahedrons). Halite is one such example.
Characterized by lattice vectors of different lengths, monoclinic crystals resemble rectangular prisms and double pyramids with a parallelogram base. Orthoclase is an example of monoclinic crystal.
All the three vectors of such crystals are asymmetrical having different lengths; hence, they are named triclinic. As a result, these crystals have strange shapes. Microcline is a triclinic crystal.
Similar to cubic crystals, trigonal crystals have a stretched body possessing a 3-fold axis of rotation, instead of the 6-fold axis of the hexagonal division. Dolomite is one such trigonal crystal.
Tetragonal crystal is another crystal similar to cubic with the difference being a stretched lattice vector to a certain length. In short, a tetragonal crystal looks like a rectangular prism with a square shaped base. Wulfenite is an example of tetragonal crystal.
Orthorhombic crystals are rectangular in cross section with rectangular prisms and pyramids. When viewed from the side, an orthorhombic crystal resembles a tetragonal crystal. Aragonite is one such orthorhombic crystal.
As suggested from the name, a hexagonal crystal is a six-sided prism. However, when you look from the cross section, you will notice a regular hexagonal shape. An example of hexagonal crystal is beryl.
On the Basis of Properties
The molecules of such crystals are bound together through strong ionic or electrostatic forces. Ionic crystals are generally hard and have high melting points. Sodium chloride (NaCl) is an example of ionic crystal. Both sodium ion and chloride ion are held together with non-covalent, electrostatic bonds.
Covalent crystals have real chemical bonds between all the atoms of the crystal. Thus, a single crystal of a covalent crystal is a single large molecule. Diamond, considered to be the most precious crystal, is one such example.
The atoms in metallic crystals are placed on lattice sites while the outer electrons move freely around the lattice. Such crystals generally have very high melting and boiling points. Nickel and copper are metallic crystals.
Molecular crystals are characterized by weak and non-covalent bonds, such as hydrogen or van der Waal’s forces. Such crystals are usually very soft and have low melting points. Sugar is a typical type of molecular crystal.