Cubic Zirconia also known as CZ is a diamond stimulant.
A diamond stimulant is something that looks like a diamond but is not a diamond. Do not confuse a stimulant with a synthetic diamond which is actually a diamond whereas a stimulant is not a diamond.
CZ is chemically known as zirconium dioxide (ZrO2). It is manufactured fairly cheaply and looks very similar to a diamond so it is used in almost all cheap jewellery.
Commercial manufacturing of CZ started in 1977. One of the techniques to manufacture CZ uses a technique known as skull crucible where the material (in our case zirconium oxide) forms its own crucible. This is done due to the very high melting point of CZ.
Normally CZ is colourless but to obtain colours it can be doped using various elements. Cobalt to get a blue colour or Iron to obtain a yellow colour.
Cubic zirconia does not last a lifetime, it is easily scratched and starts to become cloudy as it starts taking in oils. You have to really take good care of cubic zirconia jewellery to make it last.
CZ is a cheap alternative to a diamond. It has no investment value and virtually no resale value. If you need a ring which looks like a diamond ring and want to buy it at a cheap price then you can consider a CZ ring but a diamond ring is a diamond ring and a diamond is forever. It is not every day that you will be buying a diamond, in many cases it is once or twice in a lifetime then why not go in for the real thing; Buy that diamond.
Simply speaking hardness is resistance of a material. One method of measuring hardness is using the Mohs hardness scale. This scale gives rating to minerals on their ability to scratch softer minerals.
CZ has a rating of 8 compared to 10 a diamond. So a diamond is harder than a CZ. The edges in a diamond always remain true and sharp whereas in a CZ they are dull. Also in a diamond you can never see polish marks but in a CZ the polish marks are visible. These differences are due to the difference in hardness.
This means that over time CZ will wear away and will need to be replaced which is not true for a diamond.
Refractive Index is a number which describes how light propagates through a substance. When light enters a diamond or a CZ it bends, gets reflected and creates a kind of brilliance. CZ has a refractive index of 2.15 whereas diamond has a very high refractive index on 2.42. Therefore a diamond will sparkle much more than a CZ.
To understand dispersion consider the rainbow. Here white light passing through a prism gets dispersed into different colours. In a diamond fire is the term used to describe its dispersive nature. The facet angles and quality of polish all add to the fire or dispersive nature of a diamond. In CZ this is very high (0.066) exceeding that of a diamond (0.044). This often leads to CZ having a rainbow effect instead of a real fire which we see in a diamond.
Cut & Clarity
CZ because of their being manufactured in a laboratory are nearly always flawless and colourless (unless they are deliberately coloured). Flawless diamonds on the other hand are very difficult to find.
CZ is a thermal insulator whereas diamond is a thermal conductor. Thus for testing purposes this can be a method to find out the difference between CZ and a diamond.
Density of a substance is its mass per unit volume. Mass is related to weight so this means that the weight of a diamond and CZ are different; In fact CZ is about 1.7 times the weight of a diamond. We can also use this property to test the two stones by sinking them in heavy liquids. Diamond being lighter will sink more slowly.
For your information the density of diamond is 3.51 gm/cm3 and the density of CZ is 5.5 gm/ cm3.