[meteorite-list] Meteor crater impactite?

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 09:54:08 2004
Message-ID: <3C76626D.DB2E622_at_lehrer1.rz.uni-karlsruhe.de>

Graham wrote:

> A friend brought me a very interesting rock that he found about
> 1/2 Km from the rim of the crater. It is porous like lava but it
> seems denser than most lava that I have seen.

> It is dark b r o w n i s h -red and
> it has globs of sand fused to it.


Hello Graham, Mark, and List,

Which part of the rim, because:

"... these dark b r o w n and weathered glasses were collected
... s o u t h e a s t rim of Meteor Crater ... we infer that the
glasses examined so far are mixtures of material from the topmost
(Moenkopi) and the underlying (Kaibab) terrestrial layers with the
impactor. [MA P. et al. (2000) Nickel-59 in impact glasses from
Meteor Crater, Arizona: Implications for the cratering process
(MAPS 35-5, 2000, Suppl., A100).]

> it has globs of sand fused to it. When I looked at the fused
> sand with my 10x magnifier I noticed that the sand grains
> are partly melted into each other.


> It is p o r o u s like lava but it seems denser ...

The glass fragments are found in the impact ejecta from the
Meteor Crater as aerodynamically shaped, centimeter-sized
masses of v e s i c u l a r glass that contain micrometer-
sized spherules of Ni-rich metal. They are dominated by
silica glass, but also contain unmelted quartz grains ...
[BOUSKA V.J. et al. (1999) Metallic spherules in the impact
glass ejecta from the Meteor Crater Arizona and their origin
simulated experimentally (MAPS 34-4, 1999, A016)].


BUCHWALD V.F. (1975) Handbook of Iron Meteorites, Volume 2, pp. 387:

It was also shown that part of the Coconino sandstone had been
transformed to a vesicular, pumice-like material which occasionally
showed glass-like threads. Rogers (1930) described this as a
silica-glass, lechatelierite, and concluded, as did Barringer, that it
was formed by shock melting of the quartz sand upon the meteoritic
impact, in other words was a true impactite somewhat similar to those
from Henbury and Wabar. Nininger (1952a; 1956) later collected and
examined large numbers of impactites. The metamorphosed sandstone
grains were found to be stained by iron oxides, presumably because
they had become coated with metal from the iron-nickel vapor.

> It looks like it has chips and pieces of small, light
> rock in it. Could these be fragments of limestone ...?

SHOEMAKER E.M. and KIEFFER S.W. (1974, 1979) Guidebook
to the Geology of Meteor Crater, Arizona (Publ. No. 17, Center for
Meteorite Studies, Arizona State University, Tempe, Arizona, p. 15):

Shocked Sandstone

Shock metamorphosed Coconino Sandstone was first recognized at
Meteor Crater by Barringer (1905), Tilghman (1905) and Fairchild
(1906). These investigators recognized three main types of shock
metamorphosed specimens:

1) crushed and pulverized sandstone;

2) compressed rock with a higher density than the original
sandstone and a s l a t y structure (called Variety A by
Barringer); and,

3) cellular pumiceous lechatelierite which floats on water (called
Variety B). In the Variety B rocks, Rogers (1928) recognized grains
of silica glass which retained the structure of the sandstone from
which they formed and which he called "paramorphs of lechatelierite
after quartz." Chao (1967) and von Engelhardt and Stöffler (1968)
have recognized glass with the same property and refer to it as
diaplectic or thetomorphic glass.


Best regards,

Bernd
Received on Fri 22 Feb 2002 10:23:25 AM PST