From Dave Kisor:

Re: Martian “Yellowstone” might have nourished life (May 22, 2008): Sand is a particle size and not a specific mineral. Most terrestrial sand is made up of broken down granite (and other larger grained mineral intrusives) and what usually arrives at the beach are quartz particles, whereas Martian sand is predominantly basaltic. On Earth, basaltic sand beaches are usually on oceanic islands and the sand is said to “bark” under your feet, but it sounded more like a squeaks and crunches to me.

Dave Kisor
Naval Veteran and Geographer

(Editors’ note: The Columbia Encyclopedia, Sixth Edition characterizes sand as: “rock material occurring in the form of loose, rounded or angular grains, varying in size from .06 mm to 2 mm in diameter. ... Its most abundant mineral constituent is silica, usually in the form of quartz. ... Many other minerals, however, are often present in small quantities. ... Some sands—e.g., coral sands, shell sands, and foraminiferal sands—are organic in origin.”)