A white gemstone is much less expensive than a diamond. However, diamond substitutes, including cubic zirconia, cannot imitate the light-dispersing properties of a diamond, according to Robert Hazen, a research scientist at the Carnegie Institution of Washington’s Geophysical Laboratory. The white light that is produced by a diamond occurs when light enters a faceted gemstone from every side and then bounces back and forth inside the gem before it shoots back out. Each color reflects and bends differently inside a diamond. When colors separates this is called dispersion. Other gems cannot equal the diamond's light-dispersing properties.
No stone looks exactly like a diamond, but the sapphire and its properties come close. The white sapphire’s refractive index is a bit lower than that of a diamond. When looking at a true diamond you can see colors in the faceting. When looking at white sapphire you will see white light reflected in the faceting, explains Awesomegems.info. When the white sapphire is of fine quality is it without color and appears to be a one carat diamond, but doesn’t cost anywhere near what a diamond would cost. Colorless sapphires have long been used as a substitute for diamonds.
White topaz is a good alternative. When topaz is colorless and see-through this means that is it pure topaz. Typically topaz is reddish-orange or yellow, but it can be transparent and look similar to a diamond.
Cubic zirconia (CZ) is a synthetic gemstone that is made in a lab. It imitates the look of a diamond. CZ can look so much like a diamond that it is hard to tell the difference without the use of a jeweler’s loupe (magnifying glass). CZ, unlike a real diamond, is flawless. Diamonds have both external and internal flaws. The CZ will sparkle less than a diamond. Sparkle is the measure of the amount of light that is reflected by a diamond when it is seen from various angles. However, a CZ is brilliant or "fiery," but this can result in a synthetic effect.
Zircon is another alternative to diamonds. It is not to be confused with cubic zirconia, which is synthetic. Zircon is a natural gemstone with light refracting qualities that are often better than that of a diamond. It is white or colorless, but not as hard as a diamond or a sapphire.