[meteorite-list] Distinguishing volcanic from impact glasses

[Jean Alix Barrat]

To differentiate between volcanic glasses and impact glasses is a 
classical problem that has been addressed by those who have studied 
glass beads found in lunar soils. For the latter, the homogeneity of 
chemical compositions within a bead is a very good criterion (except for 
volatiles). The glass beads which are impact melts are very 
heterogeneous. This is also the case for glass beads found in howardites 
and which are always impact melts. In terrestrial cases, it is a 
question that has been treated many times, especially for South American 
glasses (example of calites and macusanites). A lot of data have been 
obtained (I remember a thesis defended in Grenoble in the years 1995 
under the direction of Gérard Poupeau who was interested in fission 
tracks, and who considered using some of these glasses as standards). 
There is a really simple criterion to distinguish these glasses, and 
there must be references (I think by Christian Koeberl if my memory is 
correct). Glasses like calites or macusanites are rhyolitic. This type 
of lava contains measurable amounts of water. In contrast, impact 
glasses (even of rhyolitic composition) contain ridiculously small 
amounts of water. This is an excellent criterion to make the difference.

Best regards,

Jean-Alix

Le 05/03/2022 à 20:53, Paul via Meteorite-list a écrit :
> Ferrière, L., Crósta, A.P., Wegner, W., Libowitzky, E.,
> Iwashita, F. and Koeberl, C., 2021. Distinguishing
> volcanic from impact glasses—The case of the Cali glass
> (Colombia). Geology, 49(12), pp.1421-1425.
> https://www.researchgate.net/publication/354386557_Distinguishing_volcanic_from_impact_glasses-The_case_of_the_Cali_glass_Colombia 
>
>
> More papers by Dr. Crosta at:
> https://www.researchgate.net/profile/Alvaro-Crosta/research
>
> Another paper about impact glasses is:
>
> Schultz, P.H., Harris, R.S., Perroud, S., Blanco, N. and
> Tomlinson, A.J., 2022. Widespread glasses generated
> by cometary fireballs during the late Pleistocene in the
> Atacama Desert, Chile. Geology, 50(2), pp.205-209.
> https://pubs.geoscienceworld.org/gsa/geology/article/50/2/205/609354/Widespread-glasses-generated-by-cometary-fireballs 
>
>
> Yours,
>
> Paul H.
>
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