The science of Crystle is called Crystallography. Crystallography is Important, as it is the foundation upon which Gemmoligical knowledge is based. The properties by which gemstones are identified are so bound up their crystals is absolutely necessary. The fundamental principles set out in this chapter are interwoven the entire subject of gemology.
During the snow formation of minerals, which ultimately from rocks, atoms of different elements come together and arrange themselves in a pattern depending upon the force acting on these atoms. This regular arrangement of atoms in a definite orderly manner ultimately results in a framework or lattice of atoms. When this framework develops in a regular manner, then it gives rise to a structure, which has a smooth surface and geometrical form- this structure is called a Crystal.
A substance in which the constituent atoms, ions, or molecules are arranged in accordance with a definite regular structure throughout. Under favourable conditions, this regularity of internal structure gives rise to a symmetrical external form bounded by plane surfaces known as crystal faces.
ELEMENTS-ATOMS-MOLECULES-COMPOUNDS AND MANY COMPOUNDS COME TOGETHER AND MAKE MINERALS AND MINERALS COME TOGETHER AND MAKE A CRYSTAL OR ROCK.
A MINERAL is a uniform or homogeneous substance; which is produced by a natural inorganic process and has a chemical composition, crystal structure, and physical properties which are constant within narrow limits. Rock; on the other hand are usually matures of several different minerals. For example, quartz and feldspar, together with mica, make up the well-knows rock known as Granite.
When minerals or rocks do not have the regular internal arrangement of atoms as in a crystal, they are called AMORPHOUS. This word is taken from the Greek language and means ‘no form’ Because there is no pattern to amorphous materials, the atoms are jumbled together in small groups like the particles in a pile of sand, there is no tendency to take a definite form and consequently, smooth crystal faces are never seen.
The Chief Characteristics of Crystals are:
- Definite geometrical shape.
- An orderly and symmetrical internal arrangement of atoms.
- properties, which vary with direction such as- hardness, cleavage, the velocity of light etc.
Whereas, the chief characteristics of Amorphous Material are:
- There is no regular internal arrangement of atoms.
- they do not tend to assume a definite external form.
- Their properties are constant in all direction.
Examples of amorphous material are:
A) Amber (Organic Resin)
B) Ivory (Organic)
C) Opal (Silica Gel)
D)Pearl (Partially crystalline; Partially amorphous)
Among the natural glasses are Moldavite, Obsidian and Tektite, while the man-made, when met within jewellery, is known as ‘Paste’