" George" wrote in message ...
"don findlay" wrote in message
om...
"OndaWeb" wrote in message
...
I wrote JPl some of this yesterday. Base on what Dr. Squires has said,
it
seems clear the spherules are being exhumed out of the matrix of the bed
rock. But notice they are relatively scarce in the bed rock. But on
the
surface, epically outside of the crater, they are plentiful, virtually
covering the entire surface.

Thus it seems that the bedrock, thought to underlie the entire plain in
Meridiani, must be filled with these spherules that are eventually
"released" as the bedrock is eroded by wind. Perhaps the bedrock
becomes
the dust and sand of Mars. The spherules are left behind, at least in
this
area, to blanket the floor (or they may be blown and rolled from
somewher
uphill).

And it seems likely the spherules are the source of the hematite.
According
to the "mineral map", wherever the spherules are, the hematite signature
is
strong (at the rim of the crater, outside the crater, some places
inside.)
Conversely the signature is weak where there are few spherules (in the
bedrock, where the spectra of the soil was taken, and most
significantly,
where the airbags of the Lander squashed them into the soil).

It seems to me the easiest explanation is fine volcanic ash (maybe
cemented
with some water from snows when the orbital eccentricity changes)is the
bed
rock and the spherules are hematite rich condensed globules. So any
geologist know of a plausable process by which a volanic eruption would
make
both ash and hematite rich spherules?

The rocks look for all the world like Archaean rhyolitic ignimbrites
(colour, platy parting and all). Spherules are characteristic;
coalesced pairs common.
http://users.indigo.net.au/don/pr/dogsballs.html (sometimes in
threes)
(The haematite would be unusual though. )

The spherules are a puzzle (to me). The spherule texture is little
different from that of the matrix.

df.



Can you post a link to some pictures or description of archaean rhyolitic
ignimbrites that look like what we are seeing on Mars? I don't doubt you
Don, but that kind of thing just isn't found in my neck of the woods, so I'd
like to see an example. TIA.

Link? No, unfortunately. They'd be just rhyolites to the survey.
Otherwise known as "ringing rock", which rhyolites generally are. You
can have great fun playing tunes on them, and cut slices ring like
tubular bells (glass).
Google up search terms "bipyramidal quartz" ignimbrite rhyolite flows
flow spheres spherical etc. Given the quartz, the whorly ignimbritic
texture, and the glass-like nature of the rock, the spheres seem to be
some sort of growth in an incandescent state (maybe it rained or
something, and caused nucleation (of what though?) , and the spheres
got entrained in what might have been some sort of gas flow). Because
they do occur in trains..

The spheres I'm thinking of (which are unusual in rhyolites generally,
but common in these particular units) are lithic. But having seen the
rhyolitic-looking rocks in the mars pics (long shot though and should
be able to qualify), spheres of pyrite (which don't occur in them) did
nevertheless come to mind. You see pyrite spheres in funny things,
and the alteration to haematite figures I guess.