Granitic rocks on Mars!
Here is what I told my kids - (although not a geologist, but decades working in prospecting, exploration and mapping):
The white rock is absolutely amazing!
Look at all the others. They are glassy, vuggy - volcanic looking with air pockets and slidy shiny sides.
The white one has black crystal like growths - pyroxene crystals (?) -as suggested in the NASA linked paragraph; found in a white mass. It looks like granite.(Silica based?) Which is a deep under 'earth' slow growth rock - as opposed to the volcanic looking ones which are faster cooling surface rocks.
Like the granite of New Hampshire, deep, old rocks exposed to the surface by millions of years of erosion. (Or the uplifting of deep rocks, on the west coast)
How did it get there? If it was on earth, you could say glacial transfer and deposition. And why is it broken? Freshly exposed inside with sharp edges?