THOMAS LIVINGSTON MITCHELL
1792-1855
​AND

CHARLES DARWIN
​1809-1882

Written By Aubrey Whymark 2017
Sir Charles Darwin, well known as the first person to describe an Australasian tektite in western scientific literature, also carried out some obscure work on natural selection. Yes, the first Australasian tektite, a broad-oval flanged button measuring 26 x 22 x 7 mm, was published by Charles Darwin in his 1844 book 'Geological Observations on the Volcanic Islands visited during the Voyage of the H.M.S. Beagle'. Here is what Charles Darwin said:

Obsidian Bombs

Many of the first tektites described were considered to be obsidian bombs. The terms 'obsidian bomb' 'obsidian button' and 'obsidianites' were in common usage up until the 1930's. They were considered to be volcanic in origin.
 
ABOVE: Charles Darwin's description of an obsidian bomb in his 1844 book 'Geological Observations on the Volcanic Islands visited during the Voyage of the H.M.S. Beagle'.
So, what is clear is that Sir Charles Darwin was presented with an Australite by Sir Thomas Mitchell. What we are not so sure on are the timings and from where the Australite came. This is what we know for sure:
07 April 1835, returning to Sydney on the 14 September 1835: Mitchell's Second Expedition. The aim of the expedition was to trace the course of the Darling River to the sea: This was not achieved.

12 January 1836: H.M.S. Beagle, with Darwin aboard, arrived at Sydney Harbor, Australia. It is not known if Mitchell met Darwin in Sydney - it is possible, but the timing is tight.

16 January 1836: Darwin went on an inland trip to the Blue Mountains and Bathurst, New South Wales.

27 January 1836: Darwin arrives back in Sydney.

30 January 1836: H.M.S. Beagle, with Darwin aboard, sets sail.

05 February 1836: H.M.S. Beagle arrived at Hobart Town, Tasmania.

17 March 1836, returning to Sydney early November 1836: Mitchell's Third Expedition: The aim of the expedition was to trace the course of the Darling River. On 23rd May 1836, he reached the Murray River. He then followed the Murray River. He discovered the Grampians and then followed the Glenelg River to the sea.

02 October 1836: Darwin arrives back in England.

19 May 1837: Thomas Mitchell travels to London, England, after applying for 18 months leave.

July 1838: Mitchell obtains a further 12 months leave.

31 May 1839: Darwin writes to Mitchell:

To T. L. Mitchell 31 May [1839]

   My Dear Sir

   I am extremely obliged to you, for your great kindness in making enquiries respecting my servant.- But by a great chance, the day after I saw you, I made an arrangement for him to work his passage out as a cook to a vessel. I am very sorry you should have taken so much trouble in vain.-

   I enclose the curious stone, which I take much shame to myself for not having returned earlier.- but I had stored it away so carefully, that it had utterly past from my mind. I hope before very long, however, to publish a short account of it, & the woodcut, which you permitted to be taken from it.-

   Believe me. Very truly yours, Chas. Darwin

   12 Upper Gower Street, May 31st

1939: Mitchell is awarded a knighthood.

March 1840: Mitchell requested a further six months leave, was granted three and ordered to leave England by 18 June. He nevertheless was arrested, narrowly missed being imprisoned for debt in London on 8 August and did not reach Australia till 1841.

REFERENCES:
https://en.wikipedia.org/wiki/Thomas_Mitchell_(explorer)
http://adb.anu.edu.au/biography/mitchell-sir-thomas-livingstone-2463
http://majormitchellexpedition.com/t-l-mitchell/about-thomas-mitchell/
https://www.aboutdarwin.com/timeline/time_04.html#0090
http://majormitchellexpedition.com/wp-content/uploads/2010/04/Stapylton-Book-Volume1.pdf

ABOVE: Mitchell's expeditions. Source: Wikipedia

Magic Stones

Aboriginal people had known about tektites for a long time. They were utilised as magic stones / talisman and flaked to be used as tools. Darwin became the first person to describe an Australian tektite in western literature. The Aboriginal people paid a high price during Mitchell's expedition, which somewhat tarnishes this discovery.
 
OK, so two scenarios present:

Mitchell found the australite on his second major expedition between 07 April 1835 and 14 September 1835. He met Darwin in Sydney and gave him the australite.

OR

Mitchell found the australite on his third major expedition between 17 March 1836 and early November 1836. Mitchell then brought it with him to London and lent it to Darwin (probably) in 1838. (Mitchell may or may not have met Darwin in Sydney).


The latter scenario is more probable. The article below gives valuable insight:
http://majormitchellexpedition.com/wp-content/uploads/2010/04/Stapylton-Book-Volume1.pdf

While Mitchell was alone making a survey to the southward of Lake Boga on 21st June 1836, in order to ascertain its shape, he found, near the margin of the lake - to quote from the printed journal -  ‘a small fragment of highly vesicular lava’.

The unexpected discovery was also noted briefly by Mitchell’s second-in-command, Granville Stapylton, who recorded independently in his journal:  ‘A peice [sic] of Scoria, or Lava, found near one of the Salt Lakes——’.

It is highly probable that this piece of 'lava' was the broad-oval flanged button that was lent to Darwin. Darwin certainly shared similar views that it was significant as it was a long distance from any volcano. Darwin also described it as coming from a great sandy plain between the rivers Darling and Murray. This is probably inaccurate, but would be an accurate description for the third expedition in 1836 (as oppose to the second expedition in 1835).

So the mystery cannot be 100% solved, but it looks likely that the famous Darwin australite was found by Mitchell on 21 June 1836 whilst making a journey to the southward of Lake Boga, Victoria. Salt lakes are ideal environments for finding tektites. The salt preserves the tektite and the low lying 'lakes' are depo-centers for sediments (including tektites).


So, the next mystery. The stone was returned to Mitchell on 31 May 1839. He would have received it in June 1939 in London. The stone ended up in the Natural History Museum, London. Did Mitchell sell it due to his debt or did he donate it, or did it make it's way via a third party? 

Later, the naturalist Richard Owen wrote a long series of papers on the extinct mammals of Australia based on Sir Thomas Mitchell's discovery of fossil bones in New South Wales. Could Mitchell have donated the specimen to Owen? I am speculating now!

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ABOVE: Click on the gallery above for more images. Images of the Mitchell-Darwin Australite taken in 2017 in the Natural History Museum, London. If you look at the posterior surface you can really understand the vesicular or 'cellular-structure' described by Darwin. In fact this pitting is produced by etching of the primary surface by acidic ground waters. The orange part is not original - it's probably limonite, which is often deposited around tektites in acidic waters. The glass reaction with the water will make the pH of the water surrounding the tektite more alkaline as the alkaline components of the glass are dissolved into the water. Iron oxides and hydroxides are deposited. The background grid is a 1 cm scale. Images are copyright of The Trustees of the Natural History Museum, London. They may not be reproduced without permission from the copyright owner.