Jadeite and Nephrite: the differences

 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

Crassadoma gigantea: The North American Pacific Coast "Purple-Hinged Rock Scallop"

Scallop bivalves (clams) belong to family Pectinidae, a worldwide group consisting of several hundred species, including some large northern kinds fished commercially for their edible adductor muscle. This muscle, which is used for holding the two valves together, is considered to be a delicacy by many people (Abbott, 1985).

Crassadoma gigantea (J.E. Gray, 1825) is a large scallop living in shallow waters from the Aleutian Islands, Alaska to Bahia Magdalena in Baja California Sur, Mexico. In cooler waters, it reaches its largest size: up to 23 cm in diameter and up to 20 pounds in weight). The name is derived from crassus (Latin: thick) and domus (Latin: house). The common name for this clam is the “purple-hinged rock scallop.” The internal ligament of scallops occupies a triangular pit at the center of the hinge. Crassadoma gigantea is the only species of this genus, which is endemic (confined) to this region. No records of it are known from the Bering Sea, Kamchatka, Japan, or elsewhere.

Crassadoma gigantea has as a fossil record of Miocene to Pleistocene age but only in northern California and Baja California Sur. One of its synonyms of this bivalve is Hinnites giganteus, a name no longer used because it is taxonomically out-of-date.

All of the images shown below are of same specimen (9 cm height and 9 cm width) of C. gigantea from Leo Cabrillo Beach, Los Angeles County, southern California.

 

                                     Exterior of right valve.

      End view of right valve showing the juvenile-growth region.

The juvenile part of a valve is called the “chlamys” growth stage. A juvenile lives “free” by attaching its strong byssal threads to the substrate. These threads occur on one side of the hinge, and this area (byssal notch) is usually not preserved in the adult stage. The juvenile shell, furthermore, is commonly preserved on both valves. Eventually, the bivalve becomes an adult and becomes permanently cemented to the substrate. Adult Crassadoma gigantea can attach to rock faces or pilings, as well as inside crevices and under boulders. It ranges in depth from intertidal to 80 m.

                                   Interior of right valve.

Exterior of left valve. The white encrustations are of tiny serpulid worm tubes.

                                      Interior of left valve.

Side view of both valves together (articulated), with the right valve (strongly convex) overlying the left valve (nearly flat).

The attached strongly convex right valve, is referred to as the “lower valve,” and the less convex (can be nearly flat) left valve is the “upper valve.” The terms “lower and upper,” however, are relative terms for specimens that commonly attach to vertical surfaces, like steep rock faces or harbor pilings. Permanent attachment to the substrate is rare in pectinids.

Other examples of extant-scallop genera in the world are the pectinids: Pecten, Chlamys, Aequipecten, Amussium, Crytopecten, and Lyropecten. “Wild” scallops have traditionally been harvested using scallop dredges or bottom trawls. In some areas, divers collect the scallops by hand, but this is an expensive process.

On a world-wide basis, in the last few years, there has been a decline in the numbers of “wild” scallop productivity. One reason might be the significant decline in the sharks that prey upon the scallop-eating cownose sting rays. The main diet of these rays is scallops, and without the control offered by the sharks, the sting-ray population is increasing (Milius, 2007; Schmid, 2007).

 

The simultaneous reduction in sea grasses is another contributing concern. Juvenile scallops (referred to as “spat”) attach themselves to sea grasses before seeking their adult mode of life. Sea grasses provide a sanctuary for the juveniles (Milius, 2007; Schmid, 2007).

Another reason for the decline of “wild” scallop productivity might be the rising acidity of the world’s oceans. At the root of this change is the rising carbon-dioxide levels released into the atmosphere by human activities (pollution) and forest fires. The carbon dioxide is absorbed the oceans, which are showing increasingly higher pH levels. This acidity deprives baby scallops the calcium carbonate they need to grow strong shells. Commercial shell-fishing activities all over the world are at risk, but the Pacific Northwest (especially Washington, British Columbia, and Alaska) are unusually vulnerable because winds that gust south in the summer whip deep water to the surface. These upwellings are even more prone to being acidic, because carbon dioxide tends to be trapped in colder depths (Guilford, 2014).

For more details about C. gigantea, SEE:

Coan, E.V., et al. 2000. Bivalve seashells of western North America. Marine bivalve mollusks from Arctic Alaska to Baja California. Santa Barbara Museum of Natural History Monographs Number 2 Studies in Biodiversity Number 2. 764 pp.

References Cited:

Abbott, R.T. 1985. Seashells of the world. A guide to the better known species. Golden Press, New York. 160 pp.

Guilford, G. 2014. From Our Obsession The Sea. https://qz.com/311345/the-worlds-scallops-and-oysters-are mysteriorly-dying-out/

Milius, S. 2007. Too few jaws: sharks decline let rays overgraze scallops. Science News 171(13):197.

Schmid, R.F. 2007. Shark deaths upset rest of food chain: Shark overfishing may be endangering scallop populations, say scientists. Associated Press/ABC New, May, 29, 2007.