Last year, in October, I published the following information, some of which probably needs to be updated. There has been such a flood if geological information in recent years that it's difficult to keep up -- the geologists are rolling together some of the rock types which were previously differentaited, and finding petrographic reasons for differentiating others that were previously assumed to be the same, such is the way with science. All updates gratefully received -- I will amend the list as necessary and then publish it again.
So here goes:
1. There are 31 dolerite orthostats, of which 14 have been sampled in 1991 and 2008. Some are standing stones and some are stumps. Some are spotted and some are unspotted. (I am a bit mystified as to why the unspotted dolerites do not appear on the diagrams above -- stones 45 and 62 are made of unspotted dolerite.) Rob has made the point that the differences between the spotted and unspotted dolerites are "a chimera" -- presumably on the basis that there are wide variations within the Preseli tors and other outcrops. But the latest thinking is that Carn Meini is probably NOT a source....
2. There are five crystal vitric ash flow tuffs represented in the orthostat collection. (Stones 40, 48, 46, 38, 52c. (Four distinct types?) There is not much debris to match these in the Stonehenge debitage, but similar fragments are found in the great cursus field. Research is ongoing, but they may come from the Preseli area. In the latest paper by B+I, Carn Alw is ruled out as a source location, but it is suggested that there are four other locations for similar broadly similar rock types -- as yet unidentified.
3. There are four volcanic ashes -- stumps 32c, 33e, 33f, 41d. (These are not sampled, and so all we can do is speculate...)
4. There is one calcareous volcanic ash stump -- number 40c (Again not sampled?)
5. There are 2 micaceous sandstone stumps -- numbered 40g and 42c. (More info is eagerly awaited on these......) There are also lumps of Lower Palaeozoic sandstone scatterd about in the debitage -- the largest lump weighing c 8.5 kgs. From SW Wales? Work is apparently in progress in an attempt to find the source areas for these samples.
6. There is another calcareous sandstone -- the Altar Stone (stone 80). sampled more than a hundred years ago, but not since. Probably from the Senni Beds of Carmarthenshire or Powys? (Not from Milford Haven) Interestingly, no debitage has been recognized in recent digs from this stone or from anything like it.
7. In the debitage there are lots of fragments of volcanics with sub-planar cleavage -- matching the Rhosyfelin rocks? The "rhyolite with fabric" is not all the same -- but most appears to be from the Pont Saeson area. There are NO matching orthostats.
8. There are also some basic tuffs in the collection of fragments from the debitage -- two lithologically different types. From the Fishguard Volcanics?
9. Other lithics in the stone collections from the debitage -- some stones are adventitious / introduced / modern, but some (eg haematite, greensand, slate, Mesozoic sandstones and gabbros) appear genuine, and need further research.
10. In the course of the recent geological research, 6,368 rock samples have been examined and classified -- and organized by archaeological context. the total weight of samples thus far is in excess of 70 kg. Most fragments are very small, weighing on average about 11 grams.
11. Almost half of the material in the debitage is sarsen -- I suppose we should not be surprised by that, but it would be good to know how many types of sarsen there are, and where they came from.....
12. This recent research matches pretty well with what I said in my post dated 3 December 2011:
I reckoned then that there are about 30 different rock types represented in the "bluestone assemblage" -- and unlike Rob, I give significance to the small bits as well as the orthostats, since I am interested in glacial and other processes and want to know where they came from and how they got here.
Stonehenge Bluestone Types
1. Unspotted dolerite ---- monoliths 45 and 62. Carn Ddafad-las?
2, Spotted dolerite -- densely spotted. Monolith 42 -- Carnbreseb? 43?
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?
5. Rhyolite -- stones 46 and 48, rhyolitic ash-flow tuffs. Carnalw area? Same source?
6. Rhyolite fragment from a different source from the above types
7. Laminated calcareous ash -- stumps 40c, 33f, 41d
8. Altered volcanic ash -- stump 32c, 33e?
9. Rhyolite -- another type -- stump 32e. Related to Pont Saeson / Rhosyfelin samples?
10. Micaceous sandstone -- stumps 42c, 40g (Palaeozoic -- South Wales origin?)
11. Rhyolite -- lava -- stone 46
12. Rhyolite -- flinty blue -- different lava? stone 48
13. Spotted dolerite with whitish spots --stones 33, 65, 68, stump 70a?, stump 71?, 72
14. Spotted dolerite with few spots -- stone 31, 66?
15. Spotted dolerite with pinkish spots -- stones 150, 32, 34, 35A, 35B (one stone), 39 (?), 47, 49, 64, 67, 69, 70
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
19. Silurian sandstone -- Cursus -- fragments
20. Devonian sandstone -- Altar Stone -- Devonian Senni Beds -- Carmarthenshire or Powys
21. Sarsen sandstones -- various types -- packing stones and mauls
22. Jurassic oolitic ragstone -- Chilmark?
23. Jurassic glauconitic sandstone -- Upper Greensand?
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 (see 9, 11 and 12 above. same source?)
31. Rhyolite fragments -- with titanite-albite intergrowths (source unknown)