Space/Science — HabitableZone

Space/Science » in reply to Rounded forms.

psuedomorphs
jms — (archived)

Nick and I were partially discussing the arrow and wedge shaped forms in the upper left of the MI composite photo. The rounded semi-hexagonal forms with the soft centers remind me of subhedral olivine replace by clay. Clay is still crystalline by definition, just really small crystals.

Replacement of mafic minerals by clays is a common occurance. You should be excited, because it indicates the rock in question has been exposed to water. The blobs you point out do look like clay, it is just a simpler explanation to alter a mineral in place as opposed to shoving clay into the voids (how is that done in the interior of a rock? It can happen in voids in limestones, but it never a complete proccess and requires a crack to act as a conduit) If some are thinking that after ratting, this material is oozing out of the rock, I really don't think so. It is not a little muddy spring.

Here's a bunch of pseudomorphs of olivine replaced by various other minerals. The picture are microphotographs of rocks in thin section (polarized light can pass through), so its different from the views we get from the MI, but you'll get the idea.

thumbnails

These especially caught my eye:

http://www-odp.tamu.edu/publications/187_IR/chap_12/c12_f15.htm#699343

http://www-odp.tamu.edu/publications/192_IR/chap_03/c3_f76.htm

http://www-odp.tamu.edu/publications/192_IR/chap_03/c3_f75.htm

http://www-odp.tamu.edu/publications/192_IR/chap_03/c3_f71.htm

Some nice olivine to serpentine pictures here. Again, these are thin-sections.

A macroscopic view of psuedomorphs after andalusite.

Finally, here's a pdf about thin sections and mars meteorites. The cover photo shows nice suhedral crystal forms. (euhedral = perfect crystal faces, subhedral = rounded or broken crystal shape)

Nothing here exactly like what we are discussing, but I didn't spend a whole lot of my Sunday morning on this.

jms

Log in or register to post.

The whole thread (59 posts)