HomeColours of Jadeite

Colours of Jadeite.

The mineral jadeite is allochromatic and, therefore, transparent and colorless in its pure form. Even such "pure" jadeite, however, usually appears to be white as a result of the scattering of light by fractures, openings on grain boundaries, and tiny aqueous fluid inclusions. In addition to white, jadeite comes in a variety of colors. The colors of jadeite found in Burma include a variety of shades of green ranging from very pale green to emerald-green, pale blue, pale violet or lavender, yellow, orange, burnt-sienna red, gray, and brown. Chhibber (1934: 67) provides an early description of the colors found in jadeite:

Jadeite varies from pure white to various shades of green. Not infrequently green spots or streaks are observed in the white varieties. Other less common tints are amethystine, light-blue, bright-red, brownish and black. The bright-red and brownish tints are observed in a thin outer zone of jadeite boulders embedded in red earth, and the colour is due to the dissemination of ferruginous matter by percolating water. About one-third of an inch from the surface the red colour entirely disappears. This sections of red jadeite are seen to be stained red and yellow with hematite and limonite respectively.

Guatemalan jadeite has been found in a variety of shades of green (including emerald-green blue-green) as well as lavender, mottled white and blue, light yellow, pink, and black. There is also what is referred to as "rainbow jadeite", which features several colours.

The colours in jadeite are caused by a couple of different factors. In a few instances colors are caused by mineral staining on grain boundaries. These include red-brown to orange-brown caused by hydrous iron oxides, some dark green streaks caused an iron compound, and gray or black caused by graphite staining. Most colors of jadeite, however, are due to substitutions of transition metal ions for the fundamental Al3+ and minor Mg2+ (from diopside content) in jadeitic pyroxene and the resultant presence of residues called chromophores (see Harder 1995). The emerald-green color of "Imperial Jade" or "gem jade" is due to the presence of a small amount of chromium (Cr3+). Hughes, Galibert, et al (2000: 6-7) note that "only a very small percentage of this minor element is required to induce the vivid color." Duller green colors as well as blue-green, bluish black, and blue-black jadeite are related to the presence of iron (either Fe2+ or Fe3+ or a mixture of the two). The darkest colors contain a relatively high percentage of iron oxide and closely resemble a pyroxene called omphacite. The term "leek green" is commonly applied to aggregates of jadeite and sodic amphiboles. According to Rossman (1974) and Ponahlo (1999), the lavender color is attributed to a Fe2+—O—Fe3+ intervalence charge transfer in nearly pure jadeite. The mauve color in jadeite is related to the presence of manganese.

The above discussion is based largely on studies of Burmese jadeite. Curtiss (1993: 77) provides an analysis of some of the colors found in Mesoamerican jadeite (from Mexico, Belize, Guatemala, and Costa Rica) based on spectroscopic examination:

The emerald green colour is caused by the intense absorption of blue and red light by Cr3+ contained in a small component of ureyite in a solid solution with jadeite. Some additional absorption of blue light is from Fe3+... The pale green color is caused by absorption of red light by a small amount of Fe3+ contained as an impurity in the M1 and M2 crystallographic sites of the jadeite. This absorption feature is much broader than the one produced by Cr3+; therefore, the color produced is much more subdued. The absorption of blue light is from the presence of Fe3+... The bluish green color is caused by the absence of Fe3+...

In a table on the same page Curtiss associates the following colors with the presence of the certain elements: pink with manganese2+, emerald green with chromium3+, pale green with iron2+, and brown and red with iron3+.

Burmese Jadeite. Lacroix (1930) provides perhaps the earliest detailed analysis of the composition of Burmese jadeite. Thus, he describes two stones from Tawmaw as follows. The first stone is described as jadeitic-albitite. Its composition is: 59.42% SiO2, 10.81% Al2O3, 10.69% MgO, 8.01% Na2O, 4.3% CaO, and small proportions of FeO, Fe2O3, H2O, K2O, TiO2, and MnO. The second stone is described as jadeite and amphibolite-bearing albitite. Its composition is: 66.3% SiO2, 19.94% Al2O3, 11.25% Na2O, and very small proportions of CaO, MgO, FeO, Fe2O3, H2O, K2O, and MnO. Three other stones (two from Tawmaw and one from the Kadon mine) discussed by Lacroix are categorized as amphibolites (one as amphibolite bearing chrome-jadeite). Chhibber (1934: 70), however, comments that "they are not altogether happily named" and "they are not amphibolites in the commonly accepted sense." He views them as being of "hybrid origin". The so-called amphibolite from the Kadon mine is 56.18% SiO2, 16.97% MgO, 9.18% Na2O, and 7.37% Al2O3, with smaller proportions of Fe2O3, FeO, MnO, CaO, K2O, and H2O. The second "amphibolite" contains the same elements, but in slightly different proportions: 55.82% SiO2, 21.2% MgO, 9.12% Na2O, and only 2.56% Al2O3, with somewhat larger proportions of Fe2O3 and H2O, and roughly similar proportions of the other elements. The stone described as an "amphibolite bearing chrome jadeite has the following composition: 57.52% SiO2, 13.37% MgO, 9.57% Al2O3, 8.83% Na2O, 4.5% FeO, and smaller proportions of the other elements found in the first two stones.

There have been a handful of subsequent studies of the chemical compositions of Burmese jadeite specimens. One of the more recent and most comprehensive studies is that by Htein and Naing (1994). The specimens in their sample come from the mining areas of Hpakan, Lonkin, Tawmaw, Nantmaw, Whay Khar Maw, Haungpa, and Khamti and include a wide range of colors: "from white through grey to almost black, shades of green, dark green, emerald green, lavender, yellowish through brown to reddish-brown, bluish and greyish blue-green" (page 270). Portions of the samples were subjected to X-ray diffraction analysis to determine their mineral composition. The composition of monomineralic (pure jadeite) specimens include: jadeite, jadeite ± rutile/ilmenorutile, and jadeite ± chromite/magnesiochromite ± rutile. The composition of polymineralic (impure jadeite) specimens include: jadeite + edenite + richterite ± chromite, jadeite + kosmochlor ± ilmenorutile, jadeite + enstatite + tremolite, and jadeite + tremolite + edenite + richterite + kosmochlor ± ilmenorutile. About two-thirds of the twenty-five specimens are pure jadeite and the remaining one-third impure jadeite. Next, fifteen specimens were subject to wavelength dispersive examination by an X-ray fluorescence spectrometer (page 271). The values for SiO2 range from 59.80 to 56.14, for Al2O3 from 24.18 to 15.34, and for Na2O from 15.52 to 11.65 (with one specimen containing only 5.66%). Other oxides include: Cr2O3 (1.16 to 0.03), Fe2O3 (2.34 to 0.93), MgO (one with 9.88, otherwise from 3.17 to 0.01), CaO (one with 10.84, otherwise from 5.40 to 0.33), and K2O (all <0.01). Some of the greatest variation was found in four of the specimens that were pyroxene-amphibole jades. Among the trace elements found by the X-ray fluorescence tests were Ti, Sr, Zr, Nb, Ni, and Zn (page 274). By way of conclusion, the authors note that "the present study demonstrates that jade of Myanmar may include a much wider range in mineral constituents and chemical composition than was previously recognized" (page 274).

Mesoamerican Jadeite. In his famous study of the Maya, archaeologist Sylvanus Morley (1956: 414) wrote:

a study of Middle American jades by mineralogists of the Carnegie Institution of Washington [see Washington 1922] has shown that American jades are true jadeites, though their chemical composition differs from that of Chinese jadeite. The variation is not sufficient to place them outside the true jadeite group, but it makes them differ somewhat in appearance from Chinese jades. American jade is not so translucent as Chinese [i.e., Burmese] jade; it varies from dark green to light blue-green, through all shades of gray and into white; it is more mottled than Chinese jade.

More recently, Anna Miller (2001: 29) has noted that "although some individual pieces of Guatemalan jadeite cannot be separated from their Burmese counterparts (particularly after they are worked into jewelry), the majority of materials have distinct color and often textural differences.

In the 1950s, the Smithsonian Institution's curator of geology, William Foshag, recognized (1957: 23) that Mesoamerican artifacts generically referred to as jade could be divided into four main mineralogical forms: 1) jadeite, 2) diopside-jadeite ("a mineral species of the pyroxene group of minerals, intermediate between jadeite and diopside, essentially a silicate of sodium, calcium, magnesium, and aluminum"), 3) chloromelanite ("a mineral species of the pyroxene group of minerals, intermediate between jadeite and acmite, or jadeite, acmite, and diopside, essentially a silicate of sodium, calcium, magnesium, iron, and aluminum"), and 4) nephrite. In comparing jade artifacts from various locales around the Maya area, Foshag identified seven forms: 1) the so-called "blue" jadeite associated with the Olmec, 2) the pale greenish jadeite from the Quiche region, 3) the emerald-green to apple-green jadeite found in many Guatemalan sites, 4) a gray-green jadeite frequently used for making celts (edged implements), 5) dark green chloromelanite used for making a variety of utilitarian objects, and two other types that seem to represent gradations between other types. Bishop, Rands, and Zelst (1985) have also categorized Mesoamerican jadeites in this fashion. Harlow (1993: 27) summarizes these two systems of classification and compares them to rocks found in Guatemala (see the table at the top of the following page).

The jadeite pebble found in central Mexico mentioned above has a composition of 87% jadeite, 11% diopside, and 2% acmite (Cook de Leonard 1971: 212). Another source (Borhegyi 1971: 4) also mentions Mayan ornaments from highland Guatemala being made of albite.

Bishop Type Foshag Type Guatemalan Type

Motagaua Light Types III & VI Jadeitite

Motagua Dark Type V Omphacite rock

Chrome Green - Kosmochloric omphacite rock

Chichén Green Type I? Kosmochloric jadeitite

Maya Green Type I Kosmochloric jadeitite

Costa Rican Light? Type II (Olmec Blue) Jadeitite (alightly altered)

Costa Rican Dark Type VII Omphacite rock (Motagua-II)

to black jade

Albite Light Albite Albitite 1

Albite Dark Albite Albitite 1

- Type IV Altered jadeitite

- - Albitite 2

Table 3.1: Systems of Classification of Guatemalan Jade

(after Harlow 1993: 27)

Easby (1968: 15) discusses the properties of the jadeite found in Costa Rica. She compares it to that employed by the Olmec of the Gulf coast of Mexico. The Costa Rican jadeite is described as being "amorphous rather than crystalline" with an extraordinary translucence." In terms of color, she describes the colors as ranging from "bluish to sea-green hues like those of a cresting wave." The stones often have light cloudy spots and "sometimes there are flecks or veins of the deep intense emerald green that the Chinese call... imperial or jewel jade." She also mentions (1968: 16) "an almost opaque off-white jade, finely speckled and tending toward buff, gray, or green" and states that "X-ray diffraction patterns made for two examples showed them to be composed mainly of albite, with admixture of quartz and jadeite."

A relatively comprehensive study of the composition of Mesoamerican jadeite and other "green" stones is provided by Bishop, Sayre, and Mishara (1993), who utilized INAA to study the stones (they describe their sampling techniques on pages 35-37). Their sample included 155 stones collected in the vicinity of the Motagua River valley. Archaeological specimens tested are from several sites in central and northern Belize, Chichén Itzá in Yucatan, Copán and El Cajón in Honduras, and 130 pieces are from numerous localities in Costa Rica. They divide the jade samples into seven groups: 1) Motagua Light, light green color; 2) Motagua Dark, green-black color (basically omphacite); 3) Maya Green, emerald green; 4) Costa Rican Light; 5) Costa Rican Dark; 6) Chichén Green (defined in 1985 as different from jadeite found in the Motagua River Valley, but later similar jade was found in the Motagua River Valley); and 7) Miscellaneous.

They turn first to their findings related to the first three categories. The first two of these are "easily differentiated chemically from the group of samples designated Maya Green" which have "significantly higher chromium values" (page 42). The authors also point to significant differences in the cobalt content in the three categories of stone. Overall they characterize the stones in these categories as follows (page 43):

The Motagua Light samples can be characterized as consisting of major abundances of jadeite and albite, with occurrences of prargonite and analsite... The Motagua Dark specimens contain less abundant jadeite, major abundances of omphacite, and variable amounts of analcite. In contrast, the analyzed Maya Green samples possess abundant jadeite, trace omphacite, and relatively low abundances of albite, muscovite, and analcite.

Data are provided about the chemical composition of a number of the stones belonging to these three categories (page 45). A sample of eight Motagua Light stones have the following characteristics: 58.91% Si02, 24.6% Al2O3, 12% Na2O, 1.97% CaO, 1.29% MgO, 1.01% FeO, and traces of Cr2O3, K2O, and MnO. A sample of seven Maya Green stones have the following characteristics: 57.5% Si02, 20.0% Al2O3, 10.7% Na2O, 4.78% CaO, 3.84% MgO, 1.20% FeO, 0.32% Cr2O3, and traces of K2O and MnO. A sample of five Motagua Dark Omphacite stones have the following characteristics: 53.8% Si02, 14.4% Al2O3, 6.2% Na2O, 10.36% CaO, 7.46% MgO, 2.32% FeO, 0.10% Cr2O3, and traces of K2O and MnO.

On the basis of electron beam microprobe analysis the authors plot the relative jadeite composition in the various samples (see fig. 2.3, page 49). Among the findings is that: "The Costa Rican Light specimens all lie near the pure jadeite corner, and the Maya Green are close to the jadeite-omphacite boundary." Chichén Green falls in between. Later in their chapter (page 58), the authors discuss the distinctiveness of the Costa Rican samples, which have a tendency towards a bluish-green color (like the so-called Olmec pieces), from those found elsewhere. Their distinctiveness mineralogically is related to "the virtual absence of mica and the low albite content in the Costa Rican specimens."

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