The purpose of this blog post is to provide some background concerning the generalized word “jade.” It is actually a group name, which “lumps” two different minerals: jadeite and nephrite. Although their chemical properties are different, their physical properties (e.g., hardness, specific gravity [=density], texture, color range, etc.), as well as their geologic origin and setting, can be similar and can overlap. Distinguishing between them is not a trivial matter, especially if you rely on just an “eyeball” identification.” Positive identification requires quantitative mineralogical examination(s). These could include an x-ray diffractometer, infra-red spectrometer, Raman spectrometer, and/or a petrographic microscope study of very thinly cut-and-ground sections of small pieces of the material.
Jadeite and nephrite have a moderate hardness between 6 and 7 on the Mohs Hardness Scale. Yet, they make good ring stones. This is because their aggregate structure makes them extremely tough.
JADEITE
Jadeite is a sodium-aluminium silicate [NaAlSi2O6]. It is a non-hydrous sodic pyroxene mineral. It has monoclinic crystals, a density (specific gravity) of 3.3, and greasy to pearly luster. It is very durable (tough) and difficult to break, but is not all that hard. It has a wide range of colors: apple green to deep green [the most valuable, including the “Imperial jade,” carved in China], shades of blue green, shades of pink and lavender, white (yes! even white) and also black (the rarest). Jadeite is used for making high-end jewelry and artisan pieces. Commercially important original deposits are found in Myanmar (formerly known as Burma), Cuba, Guatemala, Japan, Kazakhstan, Russia, and Turkey.
This is an image of raw jadeite that has not been cut nor polished.
(from Wikipedia 2021).
Jadeite is predominantly found in geologically complex areas called subduction zones, where convergent tectonic plate boundaries, of both modern and ancient continents, collide and where associated high pressures and relatively low temperatures occur inside the Earth’s crust to form metamorphic rocks. These rocks are commonly associated with chemically rich fluids that can partially replace some of the chemical components of jadeite; thus jadeite is rarely pure.
This is a carved piece of jadeite. Image from Wikipedia (2021).
NEPHRITE
Nephrite (Greek, meaning kidney) is a hydrous calcic amphibole silicate mineral with a formula of [Ca(Mg,Fe5Si8O22(OH)2]. It is one of the amphibole silicates. It has monoclinic crystals, a density of 2.96, and greasy to pearly luster. The crystals of nephrite are fibrous and interlock in a very strong matted texture, which is somewhat softer (thus better for carving) than jadeite. Nephrite is closely related to the tremolite-actinolite mineral group and is actually a variant of that group, whose members can be asbestos-like.
This is an ear ring with polished nephrite (7 mm height) in the center.
Nephrite is more common than jadeite. Nephrite has also a narrower range of colors (mainly green to whitish), and it is used for less expensive jewelry and artisan pieces. Its green color is commonly more subdued and darker than jadeite’s green color. It is found in South Australia, northern British Columbia, China (Xinjiang), Italy, New Zealand, New Zealand, Switzerland, Taiwan, and California.
The image above is a two-ton boulder (slabbed and polished) of nephrite from a placer deposit in south-central Wyoming. The nephrite from this locality ranges from bright green olive and black. This boulder is on display in a stairwell at the Los Angeles County Museum of Natural History.
The aforementioned metamorphic rock/suduction zone geologic setting of jadeite is similar to that of nephrite, except that nephrite forms at lower pressure than does jadeite. Nephrite is known also in placer deposits, which formed by erosion and transport from a host rock and followed by deposition elsewhere in river bottoms, along ocean beaches (California), or in glacial moraines (British Columbia).
Shown above are two abraded pebbles (largest one with a maximum length of 3 cm) of nephrite from an ocean-beach placer deposit at Jade Cove in Monterey County, California. They have a greasy feel to them.
NATURAL LOOK-ALIKES
There are many other green minerals that look like jadeite or nephrite. Some are naturally occurring (e.g., emeralds, aventurine, serpentine, olivine, smithsonite, amazonite, green varieties of garnets, etc.).
The image above is a cut-and-polished stone (28 mm height) of aventurine, which is a green microcrystalline form of quartz called chalcedony (see, via the “Search” option at the top of each one of my blogs, for my previous post on “varieties of quartz-part 1”). Although similar in color to jadeite or nephrite, aventurine is very distinctive because it has very tiny, platy mineral inclusions that occur as black dots and streaks.
IMITATIONS OR TREATMENTS
There is also the possibility that the “jade” you are thinking about buying might be is an imitation (simulant). For example, it might be a piece of green-colored plastic or resin. In some cases, pieces of nephrite have been bleached in acid to remove any unwanted brownish hue, and then stabilized with a polymer. Another possibility is that someone is trying to scam you with dyed-green calcite (= a soft mineral, easily scratched by a knife).
To protect yourself from fraud, always buy from an absolutely trusted and reputable dealer. If you are still hesitant, you can always consult a gemological association (like the Gemological Association of America or The International Gemological Institution). They use density and/or other definitive mineralogical/petrological tests, and provide you with a copy of the results; just like they do for identification of diamonds versus imitations (see one of my previous posts).
MORE INFORMATION
If you wish to obtain detailed information about jadeite or nephrite, or, for that matter, any other mineral, go to either one or both of the following websites: [note: I consulted them when writing up this blog].
www.gemdat.org
www.mindat.org
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