The Stonehenge bluestones - 46 rock types and still counting

Stonehenge bluestone No 48 -- a nice little rhyolite boulder.  Courtesy: Simon Banton

Summary:  

Below I summarise the named rock types found and analysed in Stonehenge geological studies in recent years.  At least 46 distinct rock types are now known from published articles, and within some of the categories there are other lithological / geochemical differences.  At a conservative estimate we are looking at more than 50 source sites or provenances.  Most of these are in the Preseli - Fishguard area of North Pembrokeshire.  

It cannot now be pretended that stones have been taken preferentially from the so-called "monolith quarries" at Rhosyfelin and Carn Goedog.  Not one of the known monoliths at Stonehenge has come from Rhosyfelin, and only five of the spotted dolerite monoliths MIGHT have come from the Carn Goedog dolerite sill. The very idea of bluestone monolith quarrying in Preseli is so vanishingly unlikely that it must now be dumped.  There is in any case no hard evidence in support of it. 

The bluestone monoliths and debitage "lithics" are so varied that they have to be interpreted as having come from an ancient spread of glacial erratics in the neighbourhood of Stonehenge.

I acknowledge the tremendous dedication of Drs Ixer and Bevins in drawing our attention to the characteristics of the bluestones, and pay tribute to them for their technical expertise.  On the other hand I am at a loss to explain why they have chosen to play such a prominent role in the promotion of the bluestone quarrying myth, since their own published evidence so clearly contradicts it!

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Every now and then I revisit the list of rock types represented in the bluestone assemblage in the  wider Stonehenge landscape or at Stonehenge itself.  

In spite of the abundance or papers by our old friends Ixer and Bevins, or perhaps because of it, the list does not get any easier to assemble.  There are a number of reasons for this.  

First, they refuse to classify anything as a "bluestone fragment" unless it is actually associated with one or more of the 43 known bluestone monoliths or stumps.  That is illogical and unscientific. Second, they keep on changing their labels and their rock type groups, so it's difficult to keep track of what the current thinking might be.  Third, there is a tendency to refer to anything inconvenient as adventitious or as "roadstone", often without detailed explanations of fragment sizes, shapes or find locations.  Fourth, there is a "lumping" tendency by which different rock types are grouped together under one label,  presumably because of the desire to demonstrate that monoliths (and small fragments sampled)  have come from as few quarrying sites as possible.  Fifth, there is a tendency to tie fragments found in excavations with particular numbered bluestone monoliths or boulders, even if there is no evidence that the said bluestones have been dressed or broken in any way.

If you are advocates of bluestone monolith quarrying, as Ixer and Bevins unashamedly are, it's easier to talk about two or three quarries than thirty or forty.......  But that having been said, the geologists have now accepted, in print, that the bluestones have come from multiple sources, the great majority of which are in West Wales.

So I make no apologies for the list below, which is as objective as I can make it, with many question marks used where there are uncertainties.  And I define a bluestone as any rock found at Stonehenge other than sarsen.  If it's there, its presence should be acknowledged and explained with reference to the science.

For more detail see this:

https://www.sidestone.com/books/stonehenge-for-the-ancestors-part-2

P 275.  Chapter 10.

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1. Unspotted dolerite ---- monolith 45. Carn Ddafad-las?  Unspotted dolerite Group 2.

2.  Spotted dolerite -- densely spotted. Monolith 42 -- Carnbreseb? 43?  Spotted dolerite Group 3

3. Boles Barrow dolerite -- spotted? But similar to stones 44 and 45? From Carnmeini / Carngyfrwy area?

4. Rhyolite -- stones 38, 40, ignimbrite character. Ash-flow tuffs (dacitic). Not Carnalw ? May be from different sources?  Rhyolite Group G. Or is stone 38 from Volcanic Group B? Stone 40, volcanic with sub-planar texture, now referred to Dacite Group C.

5. Rhyolite with fabric  -- stones 46 and 48, rhyolitic ash-flow tuffs. Carnalw area? Same source? Rhyolite Group F.   Stone 48 and associated fragments do mat match any known source.

6. Rhyolite fragment from a different source from the above types,  Rhyolite Group D. Now Dacite Group D?  But 8 fragments, all from different locations?

7. Laminated calcareous ash -- stumps 40c, 33f, 41d.  Volcanic Group A.

8. Altered volcanic ash -- stump 32c, 33e?  Volcanic Group A -- now Andesite Group A.  But 33e is different?

9. Rhyolite -- another type -- stump 32e. Related to Pont Saeson samples?  Rhyolite Groups A-C. (Note added: This is the foliated rhyolite described from Rhosyfelin by Ixer and Bevins -- but the link with stump 32e is speculative, being based on photographic rather than rock sampling evidence.)

10. Micaceous sandstone -- stumps 42c, 40g (Palaeozoic -- South Wales origin?)

11. Rhyolite -- lava -- stone 46.  Rhyolite Group F.

12. Rhyolite -- flinty blue, with fabric and feldspar crystals -- different lava? stone 48.  Rhyolite Group E.

13. Spotted dolerite with whitish spots --stones 33, 65, 68, stump 70a?, stump 71?, 72  Spotted dolerite Group 1

14. Spotted dolerite with few spots -- stone 31, 66? (ungrouped)

15. Spotted dolerite with pinkish spots -- stones 150, 32, 34, 35A, 35B (one stone), 39 (?), 47, 49, 64, 67, 69, 70.  Spotted dolerite ungrouped.  Considerable variations. Multiple sources.

16. Spotted dolerite -- moderate spots -- stone 37, 61, 61a?

17. Unspotted dolerite -- stone 44 -- different from stones 45 and 62

18. Very fine-grained unspotted dolerite -- stone 62.  From Carn Ddu Fach or Carn Ddafad-las. Unspotted dolerite Group 2.

19. Silurian sandstone -- Cursus -- fragments

20. Devonian sandstone -- Altar Stone -- Devonian Senni Beds -- Carmarthenshire or Powys

21. Analcime olivine basalt / dolerite -- fragments in Greater Cursus and at Woodhenge.  From W Midlands?

22. Jurassic oolitic ragstone -- Chilmark?

23. Jurassic glauconitic sandstone -- Upper Greensand? fragments.

24. Gritstone unspecified fragments (Maskelyne, Judd)

25. Quartzite unspecified fragments (Maskelyne, Judd)

26. Greywacke unspecified fragments (Maskelyne, Judd)

27. Granidiorite -- Amesbury long barrow 39

28. Quartz diorite -- ditto

29. Hornblende diorite -- ditto

30.   Flinty rhyolite -- fragments from Pont Saeson (Note: different from the Rhosyfelin samples?)

31. Rhyolite fragments -- with titanite-albite intergrowths (source unknown)

32.  Mafic igneous rock -- fragments near Fargo Plantation and near Cursus.

33.  Slaty rhyolitic crystal tuff / sparsely porphyritic rhyolite -- unblike other rhyolites.  Source unknown.

34.  Tufa fragments -- may have had a local origin in a calcium-rich environment.

35.  Altered gabbro -- source unknown

36.  Fine-grained limestone.  Road chippings?  Possibly from Mendips.

37.  Purple porphyritic lava (basalt) found in Avenue Trench 45.  Probably not roadstone

38.  Fine-grained gabbro -- not Preselite.  Source unknown -- not from St Davids Head

39.  Feldspathic sandstone -- not Devonian. Fragments.  Probably Mesozoic.

40.  Micaceous sandstone pebble (water worn)

41.  Reddish Devonian (?) sandstone -- unlike Altar Stone sandstone

42.  Medium-grained gabbro, highly altered.  Unlike other specimens.  Source unknown

43.  Altered dolerite - epidotised, sub-ophitic.  Unlike all other samples. Source unknown

44.  Altered granidiorite -- no known equivalent.  Source in the Midlands?

45.  Intermediate igneous rock -- unlike other samples -- source possibly southern Scotland?

46.  Brownish-grey Pennant sandstone (?)

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There is still confusion over the four dolerite groups as labelled by Ixer and Bevins.  Only five of the bluestone monoliths might have come from the Carn Goedog sill, or from the proposed quarrying site.  The evidence shows great lithological variety and multiple sources.

There is even greater confusion relating to the rhyolites, ashes, dacites and andesites represented in the record of rock types.

There are also various types of sarsen used as packing stones and mauls.  Some may be lumps knocked off the sarsen standing stones, but most are probably stones and boulders picked up and used locally in the construction of the stone monument and in burial mounds etc, just as many "bluestone" fragments were.  The inescapable conclusion is that the known bluestone fragments, stones, boulders and monoliths were all picked up in the neighbourhood, from a scatter derived from ancient glacial deposits.  As I have mentioned very often in the past, the great majority of the bluestone monoliths at Stonehenge  look like weathered and abraded glacial erratic boulders and slabs.  Just take a look at Simon Banton's "Stones of Stonehenge" web site!

www.stonesofstonehenge.org.uk

Here are some examples of the complex rock type labelling which we find in the geological research papers.

Some of the rather confusing re-classifications of rhyolites and volcanics.

Changes in nomenclature, summarised by Ixer and Bevins, 2022, Ch 10 in Vol 2 of "Stonehenge for the Ancestors".

The 8 rock type groups identified as bluestone fragments in Stonehenge excavations (Ixer and Bevins 2022)