The geochemistry of obsidian provides a unique tool for both archaeologists and geologists. Geochemical data from archaeological artifacts can be matched with those from known obsidian sources to indicate the parent source of origin for each artifact, and they also may indicate the presence of unknown geological sources for obsidian. Archaeologists are interested in locating all sources of artifact-quality obsidian and in identifying geochemical types on a scale that separates geographic obsidian sources and matches them with artifacts. Archaeologists then use geochemical data to reconstruct prehistoric trade/exchange relationships and group mobility patterns through time. Geologists are interested in obsidian geochemistry (1) to understand intraflow and interflow compositional variations in order to gain insight into magmatic and flow process and (2) to compare obsidians on a regional, or global, scale to provide insight into major problems of tectonics and crustal evolution of the earth. Geochemical data are thus crucial to both archaeology and geology, but archaeological provenance studies may be compromised by a lack of knowledge about the genesis of obsidians. Obsidian sources are of several geologic types; we draw examples from Obsidian Cliffs, Oregon, and Casa Diablo, California, Borax Lake, California, Brown’s Bench, Nevada/Idaho, to illustrate, respectively, geochemical homogeneity or heterogeneity in obsidian flows, the geologic processes of magma mixing, and chemical zonation in ash-flow tuffs and to discuss the ways each geologic situation may affect provenance studies. We emphasize that appreciation of these geologic processes is requisite to sound execution of provenance analysis in geoarchaeology.

Abstract Tūhua/Mayor Island is located approximately 45 km off the NE coast of the North Island of New Zealand. This island was formed by various explosive and effusive volcanic eruptions commonly influenced by magma–water interaction eruption events occurring since the Pleistocene. The wider area of the SW Pacific contains numerous volcanic islands with a similar type of volcanic evolution. Tūhua/Mayor Island should be studied in more detail to understand the underlying volcanic mechanisms and apply this research to other volcanic islands in the SW Pacific. Mayor Island, also known by its indigenous Māori name Tūhua (obsidian in Māori), provides an ideal site for studying current volcanism. The present day island was formed around 150 ka ago and contains several rhyolitic lava-flows from different time periods, pyroclastic-flow deposits generated by small-volume localized eruptions and ignimbrite deposited by large explosive eruptions. Our research utilized a qualitative–quantitative assessment of geodiversity estimates to highlight possible geosites for the collection of precise information about the geological evolution of this area, demonstrating the potential of geoeducational sites. The term geodiversity recognizes geological and geomorphological elements, which have shaped the Earth's surface and underly our abiotic environment. Additionally, volcanic heritage was included in our equation, specifically tailored for Tūhua/Mayor Island and based on expert views (qualitative model). This model allows for a wider diversity for the area of research compared with the original method, which utilized only geological elements. The results show that areas with pyroclastic deposits exposed on the cliffs and in the centre of the collapse caldera should be considered for the further study for geosite planning.

Abstract Recent underwater archaeological surveys recovered hundreds of flint artefacts between depths of 18 and 21 m at Cala Tramontana, a small bay located in the eastern part of Pantelleria Island. Most of the flint artefacts indicate debitage, and are characterized by cores and flakes without any specific morphology. Different lithic tools were also identified, such as fragments of blades, truncations, end-scrapers, points and crested blades. An initial hypothesis is that this lithic industry represents the oldest traces of human visitation to the island, possibly related to the exploitation of the nearby obsidian source, and favoured because of the sheltered coastal configuration of Cala Tramontana and Cala Levante with respect to the dominant winds and related storms. However, the present-day coastal setting in the bay is rather inhospitable, with high cliffs and difficult marine access. In contrast, palaeo-landscape reconstructions by means of high-resolution multibeam bathymetry reveal the possible presence of a small palaeo-beach in the inner part of the bay when the sea level was 15 m lower than at present. By comparing this palaeo-sea level with the eustatic curve (and by excluding possible vertical movements), we roughly estimate an age of the lithic industry of 9.6–7.7 cal ka BP.

Abstract For at least 13 000 years, California Indians mined and worked obsidian, trading the precious volcanic glass near and far, including obsidian and its uses in their everyday lives and beliefs. The cultural importance of obsidian is emphasized by the fact that a number of tribal groups created myths specifically about obsidian. Not only do the myths illustrate tribal religious beliefs, they help to trace geological and archaeological histories, as well. That obsidian still plays economic, artistic, and religious roles in the lives of today’s Californians offers testimony to its qualities the Indians discovered long ago.