The Rocks that Don’t Belong: Macro Petrologic* Analysis of Rock Recovered from the Ness of Brodgar Excavation
Martha Johnson writes about her research into non structural and non tool rocks found at The Ness of Brodgar.
All stone is rock but most rock is not stone. In the index or glossary of most geology texts there is no listing for stone, conversely, in most archaeology texts, there is no listing for rock.
This research has been structured to include rock in an archaeological setting. As a naturally occurring material composed of crystals or grains of one or more minerals, rock is not recognized in most archaeological sites until it has been quarried and placed upright in the ground; or it has been dressed for use in a foundation or wall; or it has been struck to form a sharp edge or ground into a tool. Until a rock is a stone something; standing stone, stone wall, flaked stone axe, or ground stone mace, it is not usually recognized as a material in its own right with information to provide. On many Neolithic sites there is incidental or non-structural, non-tool rock situated at occupation levels but this material is usually not recovered and recorded as either general or small finds.
The Rocks That Don’t Belong research project is investigating the non-structural, non-tool rocks recovered from the Late Neolithic site, the Ness of Brodgar, Orkney. These rocks, termed Foreign Stone for this research, are more often found on the spoils pile than in a finds tray. It should be noted the word “foreign” used in the archaeological finds classification, “Foreign Stone,” denotes rock originating from outside the area of excavation, not from another country. The recovery, recording and identification of these rocks as discrete rock (and mineral) species will add a petrological and geological dimension to post-excavation interpretation not commonly included in most archaeological settings.
During the 2013, 2014 and 2015 excavation seasons at the Ness of Brodgar, over 2000 Foreign Stone finds were recovered. Each specimen has had the trench, structure and context recorded, their visible physical properties identified and recorded (colour, composition, texture/grain size, morphology…), and has had their specific rock (or mineral) species identified. Each specimen has also been examined for any evidence of heating.
The recording both archaeological and petrological data in this research will permit the cross referencing of rock species to structure or context. Though all rock recovered as Foreign Stone has been recorded and identified, the Foreign Stone of particular interest to this research involves those species not outcropping of the portion of the Stenness-Brodgar isthmus occupied by the Ness of Brodgar site. The recovery of these rocks at or near occupation levels, give indication of transport to the site during its period of use. Broad questions can then be asked concerning the presence of these rock species at the site.
The second portion of this research involved the compilation of all current and archival references regarding the location and description of any rock (or mineral) species found in Orkney. This species/location gazetteer permits an overall assessment of the rock types and species available within the Orcadian archipelago to people of the Neolithic. Questions can then be asked with respect to the distance(s) specific rock (or mineral) species recovered from the Ness of Brodgar could have been transported from its outcrop source(s) to the site.
Combining the knowledge of what rock species are found in Orkney and where they can be found with what rock species have been recovered from the Ness of Brodgar and where within the site they have been recovered generates the remaining post-excavation questions. Specific questions will be posed to determine if there is any concentration of a specific rock species within a structure or within a context.
*Definition of petrology: a science that deals with the origin, history, occurrence, structure, chemical composition, and classification of rocks