Abstract:While many experimental studies have been done on siliceous and metamorphic rocks for both use-wear and post depositional surface modification (PDSM) events, little is known about such experiments on volcanic materials (other than obsidian), and on basalt in particular. Here we present the preliminary results of several experiments related to: a) evidence for basalt use (e.g., butchery and fresh hide scraping) and the subsequent characteristic use-wear patterns that can be seen; and b) postdepositional surface modifications caused by bear (Ursidae) trampling on experimental basalt flakes and subsequent use of these flakes for a tumbling experiment in a special tumbling machine.The results of these experiments were compared to better understand some surface modifications noted on the Middle to Upper Pleistocene lithic assemblages of the Azokh Cave site (Nagorno Karabagh, Lesser Caucasus).Although some aspects of both events (use-wear and PDSM) remain to be studied in depth, the experiments have improved our understanding of the effects of use-wear and post-depositional trampling and tumbling on basalt lithic artefacts. In particular, it has allowed us to recognise mechanical alterations (e.g., cracks, striations, fractures, edge damage) caused by trampling and tumbling and to note differences between these modifications and those caused by use. In particular, the experiments have shown that macroscopic modifications are rarely diagnostic, especially those observed after use. Microscopic wear features such as edge rounding, polish, abrasion and striations were the most evident types of alteration on basalt flakes, although occurring at different times and from different types of use. Distribution and orientation of alterations may be key in distinguishing use-wear from post-depositional alterations on basalt artefacts.

Azokh Cave is located near the village of the same name in the Nagorno-Karabagh region of the southeastern part of the Lesser Caucasus (39°37.09' N and 46°59.19' E, 962 metres-a.s.l.). Azokh Cave and other relevant Acheulian sites in the Caucasus (Fig. 1) were described by Lioubine (2002). Together with Mousterian sites

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Chemical weathering of archaeological material is well known; however, while there have been a number of experimental studies demonstrating different types and degrees of chemical alteration on faunal remains, little attention has been paid to stone tools, and the few studies that exist relate mainly to siliceous materials and water‐induced chemical alteration. Azokh Cave, located in the South Caucasus, contains a Middle Pleistocene to Holocene infill, and detailed macro‐ and microscopic examination of the lithic assemblages recovered there indicates potential chemical weathering of the stone artefacts. The cave is also currently home to one of the largest bat colonies in the region, and their guano forms a significant component of the infill of the inner galleries. Based on these two factors, an experimental pilot study was set up to artificially chemically alter a range of stone flakes produced specifically for the task, in order to determine the nature and likely cause of weathering. The experimental flakes, produced from different raw materials, were buried in fresh bat guano for up to two years. The results reported herein demonstrate that in a relatively short time, the highly acidic composition of bat guano strongly affects calcium‐bearing rocks (e.g., limestone, basalt) altering their entire surface. Similar comparisons may be made with chemical alteration evident on archaeological lithics from Azokh Cave, suggesting that bat guano has played a significant role in diagenetic alteration.