Sandstone is a sedimentary rock that is largely made up of particles of quartz that have been bonded together with cementitious materials that are composed of such things as calcium carbonate, iron oxides, and silicaceous agents of some sort or another. There are many different varieties of sandstone, with these containing various other components such as feldspars, mica, and iron oxides like limonite. The specimen above is an example that was laid down during the Carboniferous era. Since sandstone has good architectural properties, it has been a popular building stone in large parts of the world for many thousands of years.