An article written by Alfredo Petrov is one of the best descriptions I have read to describe “Jade”. I also have his permission to reproduce this article.
There is no mineral species called “jade”. Jade is a lapidary name, applied to certain types of metamorphic rocks that are suitable for use in carvings and gemstones, and use of the name is properly restricted more to a certain special internal texture of rock than to any specific mineralogical composition. Jade has been appreciated for at least 5,000 years because of its amazing toughness, a quality that makes it possible to carve delicate features without breaking the stone. Jade is perhaps the toughest stone of all, and an intricate jade carving dropped on the floor has a higher chance of surviving the impact than any other similarly carved stone. (Notice that we are talking here about toughness, the ability to resist brittle fracture, not hardness, the ability to resist scratching – different concepts often confused by the general public; Diamond is of course the hardest mineral, but not the toughest.) Anyone who has attempted to break a boulder of jade with a hammer acquires a new appreciation for the meaning of the word “tough”.
Jade owes its toughness to the intimately interlocking texture of the microscopic crystals that comprise it. These crystals can be of several different mineral species (but usually only one, or at most two, in any given specimen). Gemologists classify jade broadly into two families: nephrite jade, composed of mineral species in the amphibole group, and jadeite jade, composed of mineral species in the pyroxene group, both groups being chemically inosilicates (chain silicates) but with different compositions and molecular structures.
Some references state that nephrite has to be composed of the tremolite-actinolite series of amphiboles, and those are by far the most common, but other amphiboles, like eckermannite, can also form nephritic jades. Jadeite jade is often stated to be composed of the mineral species jadeite, a member of the pyroxene group, but other pyroxene species can comprise “jadeite” jades too, including omphacite and kosmochlor. So now we see that the word “jadeite” has two different but overlapping meanings: a mineralogical term referring to the species jadeite (not all of which is of sufficient lapidary quality to qualify as “jade”), and a lapidary or gemological term referring to jades composed of pyroxene group minerals (not all of which are the species jadeite sensu stricto). To avoid this confusion I will use the terms “amphibole jade” and “pyroxene jade” instead of nephrite and jadeite.
To confuse the issue even more, the ever creative marketing folk have come up with numerous jade substitutes to palm off on the unsuspecting public as “jade”, and a mix of names is in use for these – any confusion being intentional. The name “Faux Jade” is of course an obvious red flag, but beware too of any sellers using terms like “New Jade” or “Jadite” (without the first e), etc., as those are also cheap substitutes that have nothing to do with real jade. Some of these substitutes are synthetic (manufactured) materials like glass and ceramic, but most are cheap soft stones, typically green or greenish, by far the most common being the minerals antigorite and lizardite, both species of the miserably soft serpentine group, as in “Lemon Jade”, “Yellow Jade”, “Andes Jade” and much of the so-called “New Jade”. Carvings of soft fragile green fluorite have also been sold as “new jade”. “Mexican Jade” is nothing more than dyed green calcite, hardness only 3, and “Alaska Jade” is pectolite, hardness 4.5 to 5.
Although soft serpentine rock is the most common false jade, there are some jade substitutes composed of much harder minerals, with Mohs scale harnesses between 6 and 7, just as in the true jades. These include various green varieties of quartz, like aventurine (“Indian Jade”), prase, chrysoprase (“Australian Jade”) and green jasper, with a hardness of 7 or close to it; translucent pale to light green prehnite, with a hardness of 6 to 6.5; bright green massive vesuvianite, with a hardness of 6.5, also known as “Californite”, “California Jade” or “American Jade”; and white to pinkish to pale green hibschite, with a hardness of 6.5, also known as “Hydrogrossular”, “Transvaal Jade” or “African Jade”; and light green or bluish microcline (“amazonite” or “Amazon Jade”), with a hardness slightly over 6. These minerals have the appropriate hardness and beauty, and are not very common, so they could be considered “semiprecious” (whatever that means), and are worthy of appreciation as good-quality lapidary stones in their own right, certainly considerably more valuable than the soft serpentine rocks, but it is still wrong to sell them labeled “jade”. Although some of them can be pretty tough, especially the chrysoprase, prehnite and hibschite, they do not have that interlocking microfiber structure that makes the true jades even tougher.
So first, how to distinguish whether your rock is really a true jade at all? Well, as we’ve already learned, for a rock to be elevated to the lofty rank of “jade”, it has to be compact enough for lapidary work, and incredibly tough. So the best instrument for testing it is not a raman spectroscope, electron microprobe, x-ray diffraction or other expensive high-tech equipment, but rather the humble hammer. OK, I’m being facetious, although there is a kernel of truth in the preceding statement.
An expert, someone who has handled many different kinds of jade and jade substitutes over a long career, can gather quite a lot of information just by looking at and feeling a stone: subtle variations in luster and surface texture that would be hard to describe to a beginner. And they have microscopes for studying the grain structure, refractometers and other instruments for measuring optical properties, spectroscopes, chelsea filters… none of which are usually part of the amateur’s toolbox (except hopefully the microscope). Even the experts can be in doubt (and when someone claims absolute certainty, one should wonder whether they really are “experts” at all), and then the only solution is to turn to a mineralogist, who will be able to use x-ray diffraction, microprobe or raman spectroscopy to confirm the mineral species present. (Remember that a mineral identification by itself does not prove jade – you also have the toughness criterion to satisfy, but you can do that with your own hammer; don’t bother the mineralogist with that!)
Nevertheless, there are a lot of other identification techniques an amateur can usefully employ. Color is the first characteristic most people notice in a stone, but it is of only limited use in identifying jades, as they can exhibit quite a range of different colors, although beginners generally “expect” jade to be green. The amphibole jades are commonly green, in many different shades, sometimes so dark as to be close to black, but they can also be white, and more rarely grey, yellowish, brown or reddish. Pyroxene jades are commonly white or light green, a lighter brighter green than most green amphibole jades, and often show patches and stringers of green in a whiter matrix. More rarely they can be blue or violet (colors associated with a small titanium content), or pink or black (the “chloromelanite” variety). As noted above, several jade substitutes show colors similar to those of real jades.
After noticing the color, the next property most amateurs want to test is the hardness – resistance to scratching. This is a good way to eliminate some of the most common soft jade substitutes, like serpentine, fluorite and calcite, all easily scratched with an iron knife blade or shard of glass (hardness 5.5), but after that it’s usefulness is rather limited. And hardness is a difficult test for beginners to do correctly; many people mistake the white streak left by a softer mineral as a scratch mark on the harder mineral! And hardness data in mineral textbooks are for individual crystal faces, not aggregates of crystals. When dragging a sharp point across an aggregate of tiny crystals, you aren’t really measuring its hardness, you’re testing its resistance to “disaggregation”, in other words its friability, or how strongly its grains are bound together – not quite the same thing as the published hardness of the constituent mineral. Furthermore, hardness is often lower on the surface of old pieces because of decomposition by weathering, and hardness also varies directionally depending on whether one is scratching parallel to the general direction of the fibers or at right angles. With all these caveats in mind, some people nevertheless claim one can distinguish amphibole jades (typically H 6 to 6.5) from pyroxene jades (normally H 6.5 to 7) by scratch tests. All I can say about that is you had better get a lot of practice with a big variety of mineral samples before you can claim any degree of reliability in hardness tests.
Since jade is a rock rather than a mineral, it is not necessarily composed of only one mineral species. The dominant component has to be an amphibole or pyroxene, but various accessory minerals can be disseminated in it. Amphibole jades often have inclusions of magnetite or other minerals; pyroxene jades often enclose albite, zircon or other species. Lack of homogeneity and the presence of inclusions of other minerals is neither proof for nor against a sample being jade.
Another test often recommended, and easily done by anyone with a good balance, is to check the density. This can be a good nondestructive way to distinguish between amphibole and pyroxene jades when dealing with a valuable artifact that one would not want to damage by scratching or by removing grains for x-ray tests. Amphibole jade has a density of 2.9 to 3.1, whereas pyroxene jade is denser, 3.2 to 3.43. Quartz and prehnite have densities lower than that of the jades, but hibschite and vesuvianite unfortunately fall within the jade range. Also keep in mind that jade is a rock, as mentioned above, so there can be some variability in density depending on accessory minerals present.
A really good way to distinguish between amphibole and pyroxene jades is the fusibility test: the pyroxene jades melt much more easily. Hold a thin splinter of the rock in the tip of a hot flame – a blowpipe or propane torch. A splinter of pyroxene jade will melt easily to a little globule of glass, but an amphibole jade with melt only with difficulty on a very thin edge.
In summary, I hope this rambling account serves the purpose of: 1) alerting beginning collectors to some of the interesting problems involved in identifying and classifying jade; and 2) inducing a healthy skepticism about any “experts” who express certainty about an identification, especially when their opinion is based merely on looking at a photo.
Addenda: A few other miscellaneous facts about jade, to be augmented later whenever some other curious factoid brings itself to my attention:
Pyroxene jades are much rarer than amphibole jades. There are maybe a hundred or more localities in the world for amphibole jade, but only about a dozen for pyroxene jade. But although amphibole jades are more common, they have the advantage of being even tougher than the pyroxene jades, being composed of even more tightly interlocking and longer fibers than the pyroxenes. The rarer pyroxene jade brings, on average, higher prices than amphibole jade, but the economic value depends more on color and translucency than it does on mineral species.
The Chinese and Japanese both started using jade roughly 5,000 years ago – amphibole jade in the case of the Chinese, and pyroxene jade in the case of the Japanese. The Chinese began to use pyroxene jade only a couple hundred years ago, after discovering the deposits in Burma, so be very suspicious of any claimed “ancient” jadeite artifacts from China – they are probably either modern, or amphibole jade. The Chinese prefer pure emerald-green jade, whereas the Japanese prefer white jade with green splotches in it, and Koreans prefer pure white jade. Americans tend to follow Chinese tastes in this regard.
Amphibole jade is called “greenstone” in New Zealand and, by treaty, all greenstone deposits, even loose pebbles in river gravel, belong to the native Maoris, so don’t dig any up without their permission.