The Altar Stone - the confirmed sample

The provenance of the Altar Stone "a grey-green micaceous sandstone which is anomalous in terms of its size, weight and lithology and which is not derived from west Wales (see Bevins et al., 2020), is currently unknown. As knocking lumps off the stones is now frowned on having a certain specimen that can be in part be destructively analysed is key to categorising and then tracing the source of the rocks.

The Altar Stone is particularly interesting as unlike the bluestones which were brought from west Wales in Neolithic time no source of such a rock is there, it comes from somewhere else.

Analysis of a labeled specimen in Salisbury Museum has confirmed that is a bit of the Altar Stone and so full analysis can be performed in confidence and hopefully we are a bit closer to finding the outcrop it was dragged from. 

Photo from the paper by Richard Bevins

"The Salisbury Museum sample 2010R.240 bears a label which, although difficult to decipher in its entirety reads ‘Portion of the underpart of the Altar Stone at Stonehenge – taken by Mr Brown of Amesbury while excavating in the summer of 1844 to ascertain if any interment there – no traces of such discovered - The search was made at the request of a Swedish gentleman who was deputed by an Antiquarian Society of (sic) Sweden to obtain the skeletons. The relics annunciate the particulars I had from Mr Brown (?) March 19, 1845 RHB.’ The rock has a second, smaller label, which states that the rock is (incorrectly) identified as being of Blue Lias age, reading ‘The Altar is of Blue Lias and incl….d about 18 in. in the gr…’. The smaller label is quite damaged and hence in part indecipherable. The attribution offers the potential for this sample to be the first, and perhaps only, sample in historic collections which provides a record of direct sampling of the Altar Stone and as such offers the possibility that this sample can be considered as a ‘go-to’ proxy for the Altar Stone itself."

From:

Assessing the authenticity of a sample taken from the Altar Stone at Stonehenge in 1844 using portable XRF and automated SEM-EDS,

Richard E. Bevins, Nick J.G. Pearce, Duncan Pirrie, Rob A. Ixer, Stephen Hillier, Peter Turner, Matthew Power,

Journal of Archaeological Science: Reports, Volume 49, 2023, 103973, ISSN 2352-409X,

https://doi.org/10.1016/j.jasrep.2023.103973

(https://www.sciencedirect.com/science/article/pii/S2352409X23001487)

(A copy of the full paper can be supplied on request to the authors.)

Abstract: Megalithic Stone 80 at Stonehenge, the so-called Altar Stone, is traditionally considered to be part of the bluestone assemblage, a diverse range of lithologies exotic to the Wiltshire Landscape. However, the Altar Stone, a grey-green micaceous sandstone, is anomalous when compared with the other (predominantly igneous) bluestones, in terms of its lithology, size and weight, and certainly in terms of its provenance. Recent investigations into the character of the Altar Stone have focussed on excavated fragments now attributed to be derived from the Altar Stone, as well as non-destructive portable XRF (pXRF) analysis on the Altar Stone itself (re-analysed as part of this investigation). In this study we have investigated a sample from the collections of Salisbury Museum, 2010K 240 (also referred to as Wilts 277), which bears a label recording that it was collected from the underside of the Altar Stone in 1844. We examined the sample petrographically and also by using pXRF and automated SEM-EDS techniques. Like the excavated fragments, this sample from the Altar Stone shows a distinctive mineralogy characterised by the presence of baryte and kaolinite along with abundant calcite cement. The presence of baryte leads to relatively high Ba being recorded during pXRF analysis (0.13 wt%). Combined, these results validate the history recorded on the specimen label and, as far as we know, makes this the only specimen taken purposely from that megalith. As such sample 2010K 240 provides a ‘go-to’ proxy for future studies of the Altar Stone as well as validating those samples recently assigned to the Altar Stone. In addition, this study demonstrates the vital importance of historic collection specimens and their preservation, conservation and documentation, as well as the role pXRF can play in the analysis of sensitive cultural artefacts and monuments that cannot be analysed using invasive or destructive techniques.