On the Habitablezone.com space bbs, a contributor named jms had earlier mentioned amygdales in regard to Opportunity rocks:

Space Sciences
The term is "amygdale"
Posted by jms on 2/24/2004 11:49:45 AM
In Reply to: Pearls? posted by RobVG on 2/24/2004 9:59:06 AM
"a gas bubble canity subsequntly filled by mineral precipitates, especially zeolites, calcite, or quartz. Often "almond shaped" (the literal meaning of the word).
They sometimes form in vertical across layering...think bubbles in beer! Often form when lava is emplaced over wet ground. More common at the top of a flow.
All that is from my geology dictionary, I'm sure other information can be dug up.
BTW, When I was teaching intro labs, I used to put a basalt that contained calcite amygdales on the rock test, really confused some students to have a basalt with calcite phenocrysts!"
http://www.habitablezone.com/space/messages/315538.html

I thought these might be a match for the smooth, dark inclusions seen in Wishstone by Spirit:

Space Sciences
Smooth inclusions in Wishstone rock.
Posted by Robert Clark on 12/31/2004 7:26:56 AM
http://www.habitablezone.com/space/messages/363418.html


Some examples:




Amygdaloidal basalt.
http://www.soes.soton.ac.uk/resource...pages/ig19.htm

Basalt lava (amygdaloidal)
http://www.earth.ox.ac.uk/~oesis/rocks/ign5.html

Amygdaloidal texture
http://www.geolab.unc.edu/Petunia/Ig...mygdule.X.html

Here's one with olivine amygdales:

Vesicular and Amygdaloidal Textures.
http://www.pitt.edu/~cejones/GeoImag...gdaloidal.html
(I thought amygdales were the result of sedimentary action. Why are these olivine inclusions still referred to as amygdales?)

photographs of meteorwrongs.
http://epsc.wustl.edu/admin/resource...rongs/m017.htm

This last site has a large collection of images of rocks that were mistaken for meteorites.

The term "aymgdale" means almond shaped but from these examples the shapes can be irregular. A problem though is that the inclusions are usually light or white colored.

Perhaps another way to identify the material of the smooth, dark inclusions is through grain size. I found this mineral classification according to grain size for *sedimentary* rocks (this works if you already know the rock is sedimentary):

Wentworth Grain Size Scale.
http://www.cliffshade.com/colorado/rocks.htm#wentworth

This gives the size for silt as 1/16 of a millimeter or 63 microns, and for clay as 1/256 of a millimeter or 4 microns. The rover Microscopic Imager has a resolution of about 30 microns, so could identify sedimentary rock of silt grain size. However, to identify clay grain-sizes you would have to use some kind of super-resolution technique:

THE SUPERRESOLVED SUPER PAN: IMPROVED RESOLUTION OF THE MARS PATHFINDER LANDING SITE USING SUPERRESOLUTION ON THE IMP SUPER PAN DATA SET.
http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1753.pdf

The technique can improve the resolution by a factor of n^(1/2) by using n images. From the Rover web pages there are many cases where multiple images were taken of the same RATted or brushed area so this method should work. You would need around 60 images of the same area to bring the resolution down from 30 microns to 4 microns. This many MI images of the same area hasn't been done before but it should be doable.
However, the Wentworth classification only works with sedimentary rock. Wishstone is very likely igneous. The question though is the mineralogy of the dark inclusions. These may be sedimentary such as amygdales for instance.
What if the grain size is found to be in the clay range of 4 microns for the dark inclusions? Could they still be igneous or perhaps metamorphic? From discussions with geologists I've only been given one type of igneous rock that could have grain sizes this low, a kind of consolidated tuff. These arise from volcanic ash fall and become solidified under high temperature and pressure.
Could Wishstone itself be tuff? Do tuff inclusions occur in basaltic rock?


Bob Clark