Limestone is widely used as a building stone because it is readily available and easy to work with. It is a sedimentary stone, layered and formed from the skeletons and shells of sea creatures that lived in vast, warm seas millions of years ago. Much domestic limestone is gray to buff in color, while some pastel shades of yellow to pink are available. Imported limestones are available in colors ranging from light beige to dark brown, red and black. When the mineral dolomite is present, it makes the limestone harder and capable of being polished in the same manner as metamorphic marble.