Composition and distinction of white nephrite from Asian deposits
Ling, Xiaoxiao; Schmädicke, Esther; Wu, Ruihua; Wang, Shiqi; Gose, Jürgen
published: Nov 1, 2012
ArtNo. ESP154019001004, Price: 29.00 €
The major and minor element compositions and textures of white nephrite samples from 6 different deposits including Xiaomeiling district (Jiangsu province, China), Luanchuan district (Henan province, China), Hetian district (Xinjiang province, China), Geermu district (Qinghai province, China), Chuncheon district (Korea) and Baikal district (Russia) were investigated by means of optical and electron microscopy and wavelength-dispersive electron microprobe analysis (EMPA). The white nephrites from all deposits display similar fine-grained textures and white color. Tremolite, as the main mineral of the white nephrite, roughly has a similar composition in all samples including high amounts of Si, Mg, Ca, and low Fe contents. Nonetheless, the samples show small but specific differences that allow distinguishing samples from different deposits. Tremolite of sample N1 from Xiaomeiling has the most extreme composition, because it contains considerably more F (average 1.8 wt.%) than all other samples, and also shows the highest Na and K contents. The tremolite of white nephrite N2 from Luanchuan shows the highest Fe content of the sample set. Its Ca content is also comparably high, while Na, K, F, and Al concentrations are below the detection limit. Tremolite of sample N3 from Hetian is characterized by the second highest F content (0.4-0.7 wt.%) and a stoichiometric Si content. Tremolite of sample N4 from Geermu has the highest nonstoichiometric Si content (∼8.1 Si pfu (per formula unit)) and a relatively high Ca content (∼2.0 Ca pfu). Other elements (Na, K, F, and Al) are below or close to the detection limit. The tremolite of Korean sample N5 from Chuncheon can be distinguished on the basis of its low F content (∼ 0.2 wt.%) and its characteristic mosaic texture. Even though sample N6 from Russia has no unique compositional feature that distinguishes it from other samples, it can be distinguished from the other samples if all textural and compositional data are combined. Our study demonstrates that fluorine of tremolite is one of the most important elements in order to distinguish white nephrite from different deposits. The Si pfu value in tremolite may be used as a further deposit characteristic. Three of the six samples (N4, N5, and N6) consistently have Si pfu values of <8, presumably caused by an intergrowth between tremolite and the Ca analogue clinojimthompsonite. The results from our study were tested on white nephrite artifacts from different archaeological sites. Our data support the hypothesis that white nephrites from Anyang Yin Ruins are derived from the Hetian district. Nephrite arts from Lingjiatan Ruins were not derived from any of the deposits investigated in this paper.