Why does my HPHT lab-grown register as moissanite on my diamond tester?

Lab-grown diamonds can sometimes be mistaken for moissanite on diamond testers due to the high-pressure high-temperature (HPHT) method used in their production. This method can leave behind metallic inclusions, such as iron or nickel, which have a much lower thermal conductivity than diamond, but similar to that of moissanite. Additionally, the crystal structure of moissanite can be similar to that of a diamond when it is grown using the HPHT method which can cause confusion for diamond testers.

Lab-grown diamonds can be grown using different techniques, including the high-pressure high-temperature (HPHT) method, which can sometimes cause them to register as moissanite on diamond testers such as the Presidium Multi Tester or Presidium Diamond Verification.

Moissanite is a mineral that has a similar appearance to diamonds and is often used as a diamond substitute in jewelry. It is also considerably cheaper than natural or lab-grown diamonds. Diamond testers work by measuring the thermal conductivity of a gemstone. Diamonds have a high thermal conductivity, which means they conduct heat very well, whereas moissanite has a much lower thermal conductivity.

However, some HPHT lab-grown diamonds can register as moissanite on diamond testers. This is because the HPHT process can sometimes leave behind metallic inclusions in the diamond, which can affect its thermal conductivity. These inclusions are often iron or nickel, which have a much lower thermal conductivity than diamond, but similar to that of moissanite. As a result, when a diamond tester is used on an HPHT lab-grown diamond with metallic inclusions, it can register as moissanite instead of diamond.

Another factor that can cause an HPHT lab-grown diamond to come up as moissanite on a diamond tester is the crystal structure. While both diamonds and moissanite are made of carbon atoms, their crystal structures are different. The crystal structure of moissanite is more similar to that of a diamond when it is grown using the HPHT method. This can cause confusion for diamond testers, as the diamond tester may be unable to distinguish between the two materials.

Moissanite is highly double refractive which means it shows extreme doubling, whereas natural and lab grown diamonds are single refractive. If you look through the table of a moissanite stone you will see two facet lines on any facet junction instead of one. With a loupe, you can therefore quickly tell if a stone is a moissanite.

In case you are not sure, it’s best to get the diamond sent to a laboratory for further verification.