Research Article Micro-PIXE Geochemical Fingerprinting of Nephrite Neolithic Artifacts from Southwest Bulgaria Ruslan I. Kostov, 1, * Christo Protochristov, 2 Chavdar Stoyanov, 2 L´ aszl ´ o Csedreki, 3 Al´ ız Simon, 3 Zita Szikszai, 3 Imre Uzonyi, 3 Bisserka Gaydarska, 4 and John Chapman 4 1 University of Mining and Geology “St. Ivan Rilski”, Sofia, Bulgaria 2 Institute for Nuclear Research and Nuclear Energy (INRNE), Bulgarian Academy of Sciences (BAS), Sofia, Bulgaria 3 Institute of Nuclear Research of the Hungarian Academy of Sciences (ATOMKI), Debrecen, Hungary 4 Durham University, Department of Archaeology, Durham, United Kingdom Correspondence *Corresponding author; E-mail: rikostov@yahoo.com Received 10 January 2012 Accepted 01 May 2012 Scientific editing by Drew Coleman Published online in Wiley Online Library (wileyonlinelibrary.com). doi 10.1002/gea.21417 Neolithic artifacts made of nephrite, Ca 2 (Fe,Mg) 5 Si 8 O 22 (OH) 2, are found at prehistoric settlements in Bulgaria. This study investigates these objects based on particle induced X-ray emission using a scanning nuclear microprobe (micro-PIXE technique). Seven nephrite artifacts from the Neolithic sites of Kovachevo, Bulgarchevo and Galabnik in southwest Bulgaria were analyzed to quantify their composition and to establish if a correlation exists between the distribution of major and trace elements, color, impurities, and texture. The nephrite artifacts are tremolite in composition, with a proposed ultrabasic ori- gin. Based on the geochemical data obtained by micro-PIXE, we divide the ar- tifacts into Group 1 objects from the Kovachevo site and Group 2 objects from the Galabnik and Bulgarchevo sites. The analytical data and microprobe analy- ses are compared with geochemical data of nephrite from across the globe. The results are in a good agreement with previous electron microprobe and elec- tron paramagnetic resonance (EPR) spectroscopy data. Our study provides a better understanding of the mineralogy and geochemistry of nephrite artifacts and helps to address questions regarding origin and the distribution of such materials in Bulgaria and other Balkan countries. C  2012 Wiley Periodicals, Inc. INTRODUCTION Nephrite [Ca 2 (Mg,Fe) 5 Si 8 O 22 (OH) 2 ] is an Fe–Mg bear- ing Ca-silicate mineral with a double-chain struc- ture, a member of the clino-amphiboles. It is a mas- sive, fibrous material with an intermediate composition in the tremolite [Ca 2 Mg 5 Si 8 O 22 (OH) 2 ]—ferroactinolite [Ca 2 Fe 5 Si 8 O 22 (OH) 2 ] series (Leake et al., 1997, 2004; Hawthorne & Oberti, 2006). It is commonly pale green or dark green in color, but can also be white, yellowish, red- brownish, or even black. In some cases, small black inclu- sions, attributed to magnetite and other spinel-type min- erals, can be found in the green fine aggregates. Nephrite genesis is commonly attributed to metamorphic or meta- somatic processes in serpentinites or dolomitic marbles (Harlow, Sorenson, & Sisson, 2007). The typical nephrite deposit is commonly found at the contacts of gabbroids, granitic intrusive rocks, or metamorphic rocks with ultra- basic rocks (Suturin & Zamaletdinov, 1984). As a decora- tive gem material, nephrite was valued by prehistoric and ancient cultures because of its durability (related to inter- nal structure) and ability to be shaped (related to the fine interlocking fibers). Nephrite and jadeite (NaAlSi 2 O 6 ), a member of the pyroxene mineral group, are frequently mistaken for one another in archaeological or historical publica- tions. This occurs because they have many of the same characteristics—particularly color, and the term “jade” was introduced when no precise mineralogical determi- nation was used. Jade comes from the Spanish “piedra de ijada” (“stone of the loin”), a name given to the green decorative mineral brought back to Europe from Cen- tral and South America by the 16th century A.D. Spanish conquistadors. Nephrite objects were widespread in Bulgaria from the early Neolithic to the late Chalcolithic period (∼6300– Geoarchaeology: An International Journal 27 (2012) 1–13 Copyright C  2012 Wiley Periodicals, Inc. 1