Irregular angular rock surfaces at Spirit site

I am admiring the Spirit/Gusev pictures and wondering if there is a
preferred shape for the large boulders that have been been blasted out
of the crater. It seems most take on an irregular angular polyhedra
shape. Thinking about it, this is the shape one would expected for
blasted and shattered rock.

http://marsrovers.jpl.nasa.gov/galle...4P2573L4M1.JPG
http://marsrovers.jpl.nasa.gov/galle...2P2575L5M1.JPG

The surfaces are marked with concoidal fractures. See ...
http://marsrovers.jpl.nasa.gov/galle...2P2574L4M1.JPG
http://marsrovers.jpl.nasa.gov/galle...ets-A080R1.jpg

Most of the surfaces I see look convex. Would not a roughly equal
number of convex and concave surfaces be expected? Where are the
counterpart concave pieces? Are these the little tiny pieces - not
the boulders?

My question: Are there any geometric rules governing filling volume
with irregular angular polyhedra?

Michael
Mars Fossils, Pseudofossils and Problematica
http://aix1.uottawa.ca/~weinberg/mars

Hi Michael, Look up "dreikanter". These are ventifacts, rocks faceted by
wind (and sand). Common in many of earth's dry locations. (deserts and
glacial). Will Estavillo
"MarsFossils" wrote in message
om...
I am admiring the Spirit/Gusev pictures and wondering if there is a
preferred shape for the large boulders that have been been blasted out
of the crater. It seems most take on an irregular angular polyhedra
shape. Thinking about it, this is the shape one would expected for
blasted and shattered rock.


http://marsrovers.jpl.nasa.gov/galle...4P2573L4M1.JPG

http://marsrovers.jpl.nasa.gov/galle...2P2575L5M1.JPG

The surfaces are marked with concoidal fractures. See ...

http://marsrovers.jpl.nasa.gov/galle...2P2574L4M1.JPG

http://marsrovers.jpl.nasa.gov/galle...ets-A080R1.jpg

Most of the surfaces I see look convex. Would not a roughly equal
number of convex and concave surfaces be expected? Where are the
counterpart concave pieces? Are these the little tiny pieces - not
the boulders?

My question: Are there any geometric rules governing filling volume
with irregular angular polyhedra?

Michael
Mars Fossils, Pseudofossils and Problematica
http://aix1.uottawa.ca/~weinberg/mars

"will e" wrote in message
...
Hi Michael, Look up "dreikanter". These are ventifacts, rocks faceted by
wind (and sand). Common in many of earth's dry locations. (deserts and
glacial). Will Estavillo

That may be true to an extent. However, as this material appears from analysis
to be basalt, it is not unusual for it to fracture in angular patterns. I've
also been looking to see if any of the rocks show evidence of columnar jointing.
So far I haven't seen any.

"MarsFossils" wrote in message
om...
I am admiring the Spirit/Gusev pictures and wondering if there is a
preferred shape for the large boulders that have been been blasted out
of the crater. It seems most take on an irregular angular polyhedra
shape. Thinking about it, this is the shape one would expected for
blasted and shattered rock.



http://marsrovers.jpl.nasa.gov/galle...4P2573L4M1.JPG


http://marsrovers.jpl.nasa.gov/galle...2P2575L5M1.JPG

The surfaces are marked with concoidal fractures. See ...


http://marsrovers.jpl.nasa.gov/galle...2P2574L4M1.JPG


http://marsrovers.jpl.nasa.gov/galle...ets-A080R1.jpg

Most of the surfaces I see look convex. Would not a roughly equal
number of convex and concave surfaces be expected? Where are the
counterpart concave pieces? Are these the little tiny pieces - not
the boulders?

My question: Are there any geometric rules governing filling volume
with irregular angular polyhedra?

Michael
Mars Fossils, Pseudofossils and Problematica
http://aix1.uottawa.ca/~weinberg/mars

I would not dismiss the dreikanters. But near and over the rim several
rocks present clear signs of coming from the ejecta blanket. The
"cone-shaped" or "funneled" morphology is typical of those rocks.

Meanwhile I would note that martian temperature and probably pressure
may play a very important role on the shaping of the rocks. Look at
this:

http://www-k12.atmos.washington.edu/..._overview.html

With such sharp drops, rocks may break in through a catastrophic
singularity. A point of failure appears and fastly expands over the
rock. As we are dealing mostly with basalt here, then the vitreous
properties of the rock would create the shapes you see.

Water may also play a local role, in certain situations, but some
inquisitive colleagues would say I'm seeing Barsooms there...

"will e" wrote in message ...
Hi Michael, Look up "dreikanter". These are ventifacts, rocks faceted by
wind (and sand). Common in many of earth's dry locations. (deserts and
glacial). Will Estavillo
"MarsFossils" wrote in message
om...
I am admiring the Spirit/Gusev pictures and wondering if there is a
preferred shape for the large boulders that have been been blasted out
of the crater. It seems most take on an irregular angular polyhedra
shape. Thinking about it, this is the shape one would expected for
blasted and shattered rock.


http://marsrovers.jpl.nasa.gov/galle...4P2573L4M1.JPG

http://marsrovers.jpl.nasa.gov/galle...2P2575L5M1.JPG

The surfaces are marked with concoidal fractures. See ...

http://marsrovers.jpl.nasa.gov/galle...2P2574L4M1.JPG

http://marsrovers.jpl.nasa.gov/galle...ets-A080R1.jpg

Most of the surfaces I see look convex. Would not a roughly equal
number of convex and concave surfaces be expected? Where are the
counterpart concave pieces? Are these the little tiny pieces - not
the boulders?

My question: Are there any geometric rules governing filling volume
with irregular angular polyhedra?

Michael
Mars Fossils, Pseudofossils and Problematica
http://aix1.uottawa.ca/~weinberg/mars

" George" wrote in message . ..
"will e" wrote in message
...
Hi Michael, Look up "dreikanter". These are ventifacts, rocks faceted by
wind (and sand). Common in many of earth's dry locations. (deserts and
glacial). Will Estavillo

That may be true to an extent. However, as this material appears from analysis
to be basalt, it is not unusual for it to fracture in angular patterns. I've
also been looking to see if any of the rocks show evidence of columnar jointing.
So far I haven't seen any.

IMHO that would happen mostly in cones or dickes. Now Mars is known
for its shield volcanoes. Mars seems to have had a very fluid magma.
So columnar jointing may be hard to find...

Hi Michael, Look up "dreikanter". These are ventifacts, rocks faceted by
wind (and sand). Common in many of earth's dry locations. (deserts and
glacial). Will Estavillo

http://www.kristallin.de/wek/windkanter.htm

I looked up "dreikanter". Those are great pictures of ventifacts.
Maybe there is a wind polishing effect going on here. However, I
think I agree more with George that the shapes are more a result of
shock and blasting.

What is columnar jointing?

Michael
Mars Fossils, Pseudofossils and Problematica
http://aix1.uottawa.ca/~weinberg/mars

"Pedro Rosa" wrote in message
om...
" George" wrote in message
. ..
"will e" wrote in message
...
Hi Michael, Look up "dreikanter". These are ventifacts, rocks faceted by
wind (and sand). Common in many of earth's dry locations. (deserts and
glacial). Will Estavillo

That may be true to an extent. However, as this material appears from
analysis
to be basalt, it is not unusual for it to fracture in angular patterns.
I've
also been looking to see if any of the rocks show evidence of columnar
jointing.
So far I haven't seen any.

IMHO that would happen mostly in cones or dickes. Now Mars is known
for its shield volcanoes. Mars seems to have had a very fluid magma.
So columnar jointing may be hard to find...

Unless it was quentched rapidly, say, perhaps in a body of liquid water?

"MarsFossils" wrote in message
m...
Hi Michael, Look up "dreikanter". These are ventifacts, rocks faceted by
wind (and sand). Common in many of earth's dry locations. (deserts and
glacial). Will Estavillo

http://www.kristallin.de/wek/windkanter.htm

I looked up "dreikanter". Those are great pictures of ventifacts.
Maybe there is a wind polishing effect going on here. However, I
think I agree more with George that the shapes are more a result of
shock and blasting.

What is columnar jointing?

http://www.gi.alaska.edu/ScienceForum/ASF6/683.html

"Pedro Rosa" wrote in message
m...
I would not dismiss the dreikanters. But near and over the rim several
rocks present clear signs of coming from the ejecta blanket. The
"cone-shaped" or "funneled" morphology is typical of those rocks.

It is my opinion that a lot of what has been seen at the Spirit site is from the
ejecta blanket.

Meanwhile I would note that martian temperature and probably pressure
may play a very important role on the shaping of the rocks. Look at
this:


http://www-k12.atmos.washington.edu/..._overview.html

With such sharp drops, rocks may break in through a catastrophic
singularity. A point of failure appears and fastly expands over the
rock. As we are dealing mostly with basalt here, then the vitreous
properties of the rock would create the shapes you see.

Water may also play a local role, in certain situations, but some
inquisitive colleagues would say I'm seeing Barsooms there...

"will e" wrote in message
...
Hi Michael, Look up "dreikanter". These are ventifacts, rocks faceted by
wind (and sand). Common in many of earth's dry locations. (deserts and
glacial). Will Estavillo
"MarsFossils" wrote in message
om...
I am admiring the Spirit/Gusev pictures and wondering if there is a
preferred shape for the large boulders that have been been blasted out
of the crater. It seems most take on an irregular angular polyhedra
shape. Thinking about it, this is the shape one would expected for
blasted and shattered rock.



http://marsrovers.jpl.nasa.gov/galle...4P2573L4M1.JPG


http://marsrovers.jpl.nasa.gov/galle...2P2575L5M1.JPG

The surfaces are marked with concoidal fractures. See ...


http://marsrovers.jpl.nasa.gov/galle...2P2574L4M1.JPG


http://marsrovers.jpl.nasa.gov/galle...ets-A080R1.jpg

Most of the surfaces I see look convex. Would not a roughly equal
number of convex and concave surfaces be expected? Where are the
counterpart concave pieces? Are these the little tiny pieces - not
the boulders?

My question: Are there any geometric rules governing filling volume
with irregular angular polyhedra?

Michael
Mars Fossils, Pseudofossils and Problematica
http://aix1.uottawa.ca/~weinberg/mars

Michael, A joint is a fracture or crack in a rock without observable
relative movement between the sides of the crack. Shrinkage joints are
caused by tensional forces set up in a rock body as a result of cooling ( in
igneous rocks this may be columnar, like those at Devil's Tower) or by
desiccation in sedimentary rocks. Sheet joints are more or less parallel to
intrusive bodies such as granite and other plutons. Tectonic joints are a
direct result of folding or thrusting of rocks and can form complex sets of
cracks depending on the rock type and resolution of forces. Joints caused by
meteorite impact radiate in a cone shape out from the point of impact. To
answer your original question: Sets of joints intersect, some at 90 degrees
and others oblique (less than 45 deg.) The result of jointing gives rocks,
clasts, of all sizes their overall shape. Once they reach the surface, then
the effects of wind, ice, water, thermal changes,biological activity, become
important to either reshape the rock or to break it down further. Hope this
helps, Will Estavillo


"MarsFossils" wrote in message
m...
Hi Michael, Look up "dreikanter". These are ventifacts, rocks faceted
by
wind (and sand). Common in many of earth's dry locations. (deserts and
glacial). Will Estavillo

http://www.kristallin.de/wek/windkanter.htm

I looked up "dreikanter". Those are great pictures of ventifacts.
Maybe there is a wind polishing effect going on here. However, I
think I agree more with George that the shapes are more a result of
shock and blasting.

What is columnar jointing?

Michael
Mars Fossils, Pseudofossils and Problematica
http://aix1.uottawa.ca/~weinberg/mars