The chromium and vanadium present in emerald produce its vibrant colour, which is stable against light and heat and so will not fade. The colour of emerald varies according to its source or location, the most desirable colour being a strong, slightly bluish green.
Colombian emeralds are pure green with a faint tint of blue. They are dichroic, which means the colour has two axes and will vary in appearance depending on the angle from which you look at it. Colombian emeralds have dominated the market for many years, but their extraction methods are thought to be causing long-term damage to the mine sites. The explosives and giant tractors used to accelerate the mining process are potentially harmful to the emeralds, which are very sensitive to shock.
Brazilian emeralds are slightly lighter in colour and contain more yellow than Colombian stones. They often have a slight cloudiness, but are mostly free of larger inclusions.
Zambian stones are a fine, deep emerald green and their clarity is good. Very few emeralds are absolutely “clean”. They often have inclusions of fibers or tremolite rods, internal cracks or irregular colour distribution, and can appear cloudy or “sleepy”. The resulting internal stresses make emeralds very sensitive to pressure. The emerald cut (or step cut/octagon) was specifically designed to maximize the valuable stone and to intensify its colour. This cut, in which the corners are removed to avoid chipping or breaking, also protects the somewhat brittle material.