The volcanic rocks used for construction throughout the Auvergne volcanoes region, as in Besse-et-Sainte-Anastaise, present a great diversity of color. They vary from the black of basalt stones to the light gray of trachytes and also have diverse nature, appearance, and properties. The volumetric mass of the rocks, 4,410 to 6,610 lbs (2,000 to 3,000 kg) per cubic meter, varies according to the density in bubbles of the magma from which they originate. As for their porosity, it depends on the more or less compact nature of their texture.