• Hardness – the measurement of resistance to permanent deformations.

On the Mohs hardness scale, the hardness of a diamond is a 10, the hardest rating of all.

  • Heart Cut See Shape.

This diamond shape has risen in popularity in the past few years. Shaped as a love heart, it is often used in engagement rings.

  • HPHT – High Pressure High Temperature treatment process.

HPHT is a diamond color enhancement process whereby the stone is subjected to high pressure and high temperatures, recreating the conditions under which the diamond was formed. While it improves the color of the diamond, it does detract from the value. Enhanced diamonds are not as rare as natural diamonds of the same color grade. A jeweler should always explain if a diamond has undergone any treatments before you purchase it.

See Color Enhancement.

  • HRD – Belgian-based certification lab.

This European diamond grading laboratory provides diamond certificates. These will detail important qualities of your stone such as color grade, clarity grade, carat weight and cut grade. Diamond certificates are particularly useful when it comes to selling your diamond, as any potential buyer will have all the information they need on the certificate. Although it is important to keep in mind that not all laboratories grade to the same standard.

  • Hue – the basic impression of a color; the aspect that gives color its identity.

In colored diamonds, a lab might give a diamond one or two or three color grades. For example, a diamond might be a fancy yellowish, brownish orange. The latter color is the most dominant hue and the one that affects the value the most.