"Timothy Demko" wrote
Close-ups like this:


http://marsrovers.jpl.nasa.gov/galle...2P2933M2M1.JPG

continue remind me of textures and fabrics I've seen in travertine and
sinter deposits.

Would sinter deposits be associated with hot springs such as in theis New
Zealand shot?

http://www.thenewzealandsite.com/photo/1413/

That "sinter terrace" does somewhat resemble the outcrop now that you
mention it. Found this definition:

Sinter: A type of fragile, commonly white or grey rock formed by
precipitation of silica from cooling hydrothermal solutions at or near a
hydrothermal vent. Precipitation of siliceous sinter (often with associated
sulfide minerals and precious metals) commonly occurs in neutral and acid
hydrothermal systems under the influence of biogenic agents such as algae
and bacteria (Cas and Wright, 1987, p. 316).


It will be nice to get some close-up spectrometry for some idea of
composition. No one has said carbonate or silica out loud yet, but I
wonder...

If the spheres are the source of the hematite, what could the host rock
possibly be?

Found this reference:

"EVIDENCE FOR AN 800 KM DIAMETER IMPACT STRUCTURE IN MERIDIANI PLANUM AND
ASSOCIATED CHANNELS AND BASINS: A CONNECTION WITH THE ORIGIN OF THE HEMATITE
DEPOSITS?"
http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1414.pdf

"The connection between the impact structures and
the origin of the hematite could involve precipitation
from hydrothermal fluids associated with the heat from
the impact, either in lakes (e.g. like banded iron formation),
or directly in the observed layered deposits."

Joe