Squires on Wishstone
From Mars on one Million Dollars a day, in Space Daily:
Jumbled textures of specimens dubbed "Wishstone" and "Wishing Well" look like the product of an explosion, perhaps from a volcano or a meteor impact. These rocks are much richer in phosphorus than any other known Mars rocks.
"Some ways of making phosphates involve water; others do not," Squyres said. "We want to look at more of these rocks to see if we can distinguish between those possible histories."
Some other speculations follow:
Monazite is a hard (5.5), dense (~5) Phosphate mineral. Rutile is a hard (6.5), dense (4.2) oxide of Titanium. Both are resistant to weathering and are found togther as sands where they've been concentrated by their physical properties. The beach enviornment is a good place for this. But wind is also a very effective sorting agent. These sediments are parented by fairly felsic igneous rocks. Lot's of these in Australia. What do you know about these sands, Nick?
Happy Birthday Spirit !