With the confirmation that a Salisbury Museum sample labelled as being from the Altar Stone matches the Altar Stone the circumstances of its collection are worth noting. I have covered most of it before:
The sample is from an 1844 excavation by a "Captain Beamish from Devonport" at the instigation of a Swedish gentleman looking for skeletons.
The obvious assumption is that Captain Beamish was a naval officer, especially as distinguished naval officers had that name - https://archivesearch.lib.cam.ac.uk/repositories/9/resources/1420 Rear Admiral Henry Hamilton Beamish, Rear Admiral Tufton Percy Hamilton Beamish, Lord Chelwood of Lewes (Tufton Victor Hamilton Beamish)
However the earliest Henry Hamilton Beamish was born in in 1829 and didn't join the Navy until 1845 and didn't become a Captain until 1864 https://www.pdavis.nl/ShowBiog.php?id=1570 (His son, also Henry Hamilton Beamish was a nasty antisemite https://en.wikipedia.org/wiki/Henry_Hamilton_Beamish ) So he isn't the Captain Beamish we are looking for.
Another branch of the Beamish family has a much more likely candidate. Richard Beamish 1798-1873.
https://www.wikitree.com/wiki/Beamish-290 for his life story - He had been a Captain in the Grenadier Guards. His obituary: https://www.icevirtuallibrary.com/doi/epdf/10.1680/imotp.1875.22714
The 1844 date hints at a connection to the Ethnological Society of London meeting of 25th May 1844 https://www.jstor.org/stable/3014114?seq=2 The members had a great interest in ancient skulls and were heavily influenced by the racist Phrenology theories of the Swedish Anders Adolph Retzius .
Richard Beamish had become a FRS in 1834 and was interested, wrote and lectured about phrenology, the study of skull shapes. His profession, however, was a civil engineer and he worked for Brunel, and wrote a biography of the great Engineer. In 1844 the first plans for what eventually became the Royal Albert Bridge over the Tamar were drawn up by Brunel and, of course, the eastern end is in the Devonport area. It seems likely that Beamish would have been in the area helping draw up the plans.
That a civil engineer was asked to lead an excavation at Stonehenge would not be unique.
Richard's brother North Ludlow Beamish had a great interest in Norse and Baltic Antiquities but was a Major and living in Ireland at the time.
So I believe it is highly likely that the Captain Beamish who excavated at Stonehenge in 1844 was Richard Beamish 1798-1873
It unfortunate that so much of the Victorian interest in Stonehenge was driven by racist theories, and even more so that temporal racism still drives many theories about the monument, in the words of Thor Heyerdahl after a sleepover at Stonehenge in 1944, "the irremediable problem with the world is that people are dumb and self-centred. This idiocy and in-group mentality results not only in industrial bloodshed and ethnocentrism, but in the superiority complex of modern civilisation over those past. Praising the genius of the Stonehengers, he ridiculed modern man’s proneness to deem his predecessors a moronic bunch."
Some of Richard's correspondence is in the Science MuseumImage used under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 Licence
Intriguingly the letter in the photograph to Richard appears to be in a very similar hand to that of the label, but that might just be a coincidence.