The latest Spirit MI composite, monochrome, from JPL.

Looks Hard. Very fine grained. With some areas of coarser material. Almost looks like "Snowflake Obsidian". Or it is probably an artifact of the RAT. Nice fracture/vein! How much lighter (less blue) is it?

How many hard rocks can this thing cut before it's teeth wear out?

Here's "Bounce" rock:

Gotta stare at this for awhile...get back to you. First thoughts are another facies of the evaporitic "Opportunity Formation". (BTW, is there an official name for this Formation? Defined as a mappable stratigraphic or lithologic unit. Convention names formations after the type locality, where it was first described. Like the Pierre Shale, the Dakota Formation, Cedar Bluffs Sandstone, etc.)