[meteorite-list] Tektites &Target rock
From: E.L. Jones <jonee_at_meteoritecentral.com>
Date: Thu Apr 22 09:43:30 2004
> Joseph Hum wrote:
> my view on this intriguing subject is that most tektites are lunar
> the reason is that if they are terrestrial what is the parent
<ahem> sand? beach, eolian (dunes), or loosely consolidated
sandstones-- under shallow seas perhaps-- pick one!
Note also the occurance of cristobalite* in Libyan Desert Glass(LDG) for
examples of target "rock" and glass formation with shocked components.
Counter argument: Why would you not make the same argument against Lunar
Material /target rock which is high magnesium silicate (pyroxenes)
Aluminum, Potassium and Sodium silicates (felsic)) and low in silicon
dioxide proper (quartz).
Counter- Counter argument: Why don't we find Stishovite in tektites? It
is a high pressure/ low temperature polymorph of quartz. The impact
formation scenario should meet that criteria. One the other hand Beta
quartz polymorphs are unstable or metastable at low pressure, therefore
it is existence is short-lived under molten temperatures and decreasing
pressure.(Especially lunar conditions) I surmise LDG must have quickly
cooled in order to have retained cristobalite.
Comments and corrections invited.
* A a high pressure form of quartz. Polymorphs of a mineral exist due
to different temperatures and pressures of formation. The form taken by
the crystal lattice is affected by how much space can be squeezed out of
the distances between atoms. For a quick discussion of those poly
morphs and meteorites, try this link: The Quartz Group< http://mineral.galleries.com/minerals/silicate/quartz.htm>
Received on Mon 09 Jul 2001 11:56:10 PM PDT