Crystallography is the study of crystals and the laws that govern their growth, external shape, and internal structure. Not only do scientists in this field study natural crystals but also the crystals formed by metal alloys, chemicals, and other synthetic materials. Often it is the use of crystallographic tools, such as an x-ray spectrometer, that find and distinguish new minerals as well as verify or correct the identification of specimens.

How can crystallography help an ordinary rockhound to identify minerals? A mineral's crystalline structure, the arrangement of its component atoms and/or ions, is responsible for the outward shape of the crystal. Rarely does one mineral form crystals that are completely unique to itself. Rather, a mineral will form crystals that are consistent with the symmetry class in which the mineral falls into, based on its own structure. Understanding what symmetry class a mineral belongs to is very helpful in identifying its crystals.

What Are Crystals?

Crystals are solids that form by a regular repeated pattern of molecules connecting together. In crystals a collection of atoms called the unit cell is repeated in exactly the same arrangement over and over throughout the entire material.

Crystals Have:

Only when a mineral is allowed to grow without interference from other minerals will it form crystals. Minerals crystallize, from many types of solutions. They may precipitate from evaporating sea water, or crystallize from magma when lava cools. While growing, minerals may develop a distinct crystal form with smooth, flat planes called crystal faces. The geometric pattern of the crystal faces reflects the internal atomic arrangement of the crystal structure. This is one of the most important things about a mineral.

 

Crystallography Reference
Amorphous	Bonds	Chemistry	Crystals
Crystallography	Crystal Systems	Elements	Isometric (Cubic)
Hexagonal	Monoclinic	Orthorhombic	Periodic Table
Symmetry	Tetragonal	Triclinic	Variations