some guesses and first impressions
Obsidian? "volcanic glass"
Basaltic composition?
concoidal fractures (macro + micro)?
possible, subtle, "cone-in-cone" impact-related structures (the "V" shaped surficial structures on the macro view)?
Light dust coating. Or cosmic radiation induced surficial devitrification?
Devitrification along fractures?
Possible fracture almost parallel to RAT'd surface resulting in strange half and half look to MI views?
Just my first impressions based upon black and white photos from a different planet. Still awaiting full filter coverage to construct cartoon color images of RAT'd surface.
Could give you "Hue 19" of the MI photos, that's all well ever get from the MI.