What is commonly referred to as jade can in fact be one of two specific types of the gemstone. The majority of the jade on sale is actually nephrite, a green stone found in China, among other countries. Then there is "true" jadeite, which is rarer and thus more valuable. Telling the difference between the two is very difficult and nearly impossible with the naked eye, though experts are able to rely on a range of tests for this purpose.
Test the hardness using specialised equipment. The hardness of various minerals is often measured on the Mohs scale, devised by the German mineralogist Friedrich Mohs in 1812. On this scale, nephrite usually registers at between 6 and 6.5. In comparison, jadeite tends to be slightly denser and harder, measuring up to 7 on the scale.
Examine the fibrous structure. Experts with the right equipment are able to tell nephrite jade from jadeite jade by looking at the specific fibrous structures of the minerals. Nephrite has a looser interwoven filtrons structure and, when fractured, can splinter or grain. When looked at under a powerful microscope, however, jadeite has a much tighter interlocking granular structure, which explains its extra toughness.
Study the differences in chemical composition. Nephrite is classified as a silicate of calcium and magnesium and is placed in the pyroxene group of minerals. Meanwhile, jadeite is a silicate of sodium and aluminium and is placed in the amphibole group of minerals due to its composition.
Look at the colour and markings. It can be very hard to tell the difference between the two types of jade by going on colour alone. Nephrite, for example, is usually dark green or grey. However, it can also be white, black or even translucent. Similarly, the colour of jadeite varies markedly due mainly to the presence of trace elements such as iron or chromium. The gem can be deep jade green, but can also be white, translucent and even black.