I think you're right; the orientation of reflective surfaces plays a big role here. If this is hematite, gray hematite that is, it's metallic luster would be a fairly reflective surface. Many of the raw images using L7, R1, and L6 filters have a number of spheroids and blocks that display this reflection. It is interesting that the reflection is mostly at the violet end of things, though. Metalic hematite can be the slightest bit bluish. (Not like a molybdenite bluish) In the other wavelengths these spots are really dark.

I've seen a couple of these blocky rocks in the outcrop, but very few of them. By Nick's report these are hematite. Rather interesting shape for a concretion. Or is there an in-situ massive hematite layer somewhere in the stratigraphy that is producing these things?

What'd be great is if I could get my hands on filters for my digital camera that are the same as the pancams. That way I could do some experiments on some samples in the rock pile. Do all metalic lusters reflect the violet end?

So that's the shark's tooth. Thanks. They've got so many names for these things! I often do the same name game with great outcrops, but never down to this detail. Glad they are having fun. The explorer's perk: you get to name everything!