sandstone
A natural sedimentary facade stone made of cemented sand grains, commonly quartz, with varied colors and textures.
Pictured: Smithsonian Castle
Sandstone is a sedimentary rock typically formed at the sites of ancient beaches or sand deposits. The rock is composed of individual grains of sand (usually quartz) cemented together. Compaction brings the grains together, and minerals such as silica, calcite, or iron oxides cement them. Under higher heat or pressure the same minerals will metamorphose into quartzite.
Sandstone is softer than many other rocks, and easily carved. As a building facade it is valued for its textural properties and attractive natural colors. Common impurities such as iron, feldspar, hematite, and mica give it a variety of different colors, including yellowish, brown, and red.
The sand grains remain recognizable within the stone. In quartzite, heat and pressure have recrystallized the sandstone into a harder mass, establishing a different stone type.