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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