Unlike sandstones, which are also composed primarily of quartz, when quartzite is cleaved, it breaks through the grains of quartz rather than through the matrix around the grains. Very hard and massive, quartzite weathers more gradually than many other rocks and, therefore, often stands out of the Earth as hills or mountains. The purest quartzite is white in color, but the rock may also exhibit a variety of other hues, such as pink, brown, blue, or gray, depending on its minor mineral constituents. The purest quartzite is frequently utilized industrially as a silica source, while those that contain impurities are more typically used as a building material.