Quartzite is a hard, massive metamorphic
rock resulting from sandstone in which
the quartz grains have recrystallized. It
is typically colored white, light gray, or yellow, but it also comes in
green, blue, purple, and black varieties that contain other minerals. Tough
and resistant to weathering it is used in road metal.
| Quartzite. Image credit: Mineral
AND PLANETARY SCIENCE