Two Materials Both Known as Jade
Nephrite jade and jadeite are two different materials both of which are commonly referred to as jade. Whilst both are metamorphic rocks nephrite jade is made up of the minerals actinolite and tremolite whereas jadeite is made up almost exclusively of the mineral jadeite. Jadeite is rarer and considerably more expensive than nephrite jade. Both stones can have a strikingly similar appearance and unless you're an expert it can be exceptionally difficult to distinguish one from the other.
The confusion between the two materials is believed to date back to the sixteenth century and stems from a misprint in the translation from Spanish to French of the original name. Despite this mistake the name jade continued to be used and is now so entrenched in common language that it would be far too difficult to start differentiating one stone from the other.
Nephrite jade and jadeite are both very tough materials and in fact nephrite is one of the toughest known substances. It's important to note that toughness and hardness are not the same. On Mohs scale of mineral hardness which is a tool that measures the scratch resistance of one mineral against another, nephrite jade grades 6 to 6.5 and jadeite 6.5 to 7 which means both can be scratched by a mineral with the same grade or a higher grade on the scale. Toughness refers to a mineral's resistance to being crushed, bent or broken.
The Chinese have been producing jadeite for over 5000 years but it's known to have been used by man for at least 10,000 years. Jade is an integral part of Chinese life and culture and some of the earliest recorded events are inscribed on nephrite tablets. Nephrite jade or nephrite as it's often known is the more common of the two.
Large deposits of nephrite jade can be found in Northern British Columbia in Canada and material from this region is often referred to as Canadian jade. Canada supplies 90% of the stone used for lapidary purposes across the world.
The photograph at the top of this page is jadeitite which is made up almost completely from the mineral jadeite. The second is nephrite jade. Both photos are clickable and redirect to the original image. Photos courtesy of James St John.