Spherical Rocks (stretched)

fragments of vessicular basalt?

fragments of vessicular basalt?

I was thinking rhyolitic pumice.

Amusingly, there are also very large scale spherical rocks, e.g. MOC image M1100944 from Malin & Edgett (2000). One is at the bottom of the striated apron, see e.g. http://www.marsunearthed.com/Articles/Channels/M1100944.htm for a smaller download.

-T

It sure looks like a large sphere. Judging by the crater above the large crater, the sun angle is from the left. This object is illuminated in a pattern opposite of the crater (in which the right lip is illuminated), so it does seem as if it's sticking up above the surface (not a crater). The gullies with little alluvial fans below sure look like water erosion. Thanks for pointing out this cool picture. I have no idea what the scale is. I guess it's from one of the orbiters.

I'm not saying that big sphere on Mars is a concretion, but when I was wondering what the heck a concretion was, I found this page that shows some big ones:

http://www.rocksforkids.com/Rocks/concretions.html

In particular, this one is amusingly large:

http://www.rocksforkids.com/images/concre4.jpg

:-) The sphere: It's a Sea Urchin fossil, and a very well preserved one at that. See the dimple in the center? That's typical. See the fuzz around the edges? That's the way they are in life, but the fuzz rarely survives to the fossil state.

:lol: If you look in the upper right portion of the picture you will see two smaller "blueberries". Each has a dimple in the center, as does the larger white one at the bottom-left of the picture.

Spherical concretions are kidney-shaped; like nodular hematite. They do not exist as single spheres and do not have "dimples". These are not concretions. These are Martian Sea Urchin fossils.

Cheatah
you are not alone in this view. there are many who believe these are fossil urchins or sponges. I find it very strange that they would be so plentiful and uniform if they were not from a biological source.
Hopefully time and research will tell.
Richard