A good diamond substitute is Cubic Zirconia.
Cubic zirconia was discovered by Two German scientists in 1937. However it was not until; the 1970's when the potential for cubic zirconia became apparent when a Russian scientist discovered process to create it in a laboratory.
From then Swarovski & Co. started to make cubic zirconia in large quantities for the diamond market.
A cubic zirconia is made is a made up of zirconium oxide and yttrium oxide and, through a complicated process of melting together the two chemicals, a radiant crystal is created. 5,000 degrees Fahrenheit are required to melt the two chemicals together but the most important part of the process is the cooling. In order to create flawless crystals the cooling process must be done correctly otherwise cracks and inclusions result.
The cubic zirconia is an ideal substitute for diamonds for those that are in a limited budget but still like to see the flash and sparkle of an apparent diamond.
It does have a little less sparkle than the real thing but has more color and fire. It weights in at about 75% more than a diamond but this is hardly noticeable until one actually weighs the stone.
Most people are unable to tell the difference between a diamond and a cubic zirconia but one way is to look at the cubic zirconia under a magnification of around 10x. You can see the facets do not point properly and where facets intersect, it is not a straight line, but the intersection is more rounded than the diamond's facets. Other ways to tell the difference are doing a specific gravity test on an un-mounted stone, marking ink on the top of the stone (the ink beads up on a cubic zirconia), when gem-printed a cubic zirconia photograph's reflective and refractive patterns, and when measuring heat conductivity, a cubic zirconia registers red on the indicator (a diamond is green).
Cubic zirconia has a hardness of 8.5 of the Mohs scale of hardness. Cubic zirconia is clear and is brilliant. Cubic zirconia comes in almost every color of the rainbow depending on the process of manufacture and despite the difference are still a very nice stone in their own right to own.
As a diamond substitute cubic zirconia more than fills the role and provides much pleasure to the wearer at an economical cost.