Inside some volcanoes, gases such as water vapor, carbon dioxide, and sulfur dioxide are dissolved within the melted rock (magma), lowering the density of the magma and increasing its buoyancy. If the magma contains a large fraction of trapped gases when it reaches the open air at the mouth of the volcano, the rapid decompression fragments the magma into pumice and ash (pieces of foamed-up magma) that explode from the volcano and rapidly harden in the air. (Think of the spray from bottles of soda or champagne if you shake them hard and open their tops.) Sometimes explosive eruptions release dangerous currents of hot gas, ash, and rock down the sides of volcanoes. These fast-moving currents, called pyroclastic flows, killed 16,000 people in the Roman towns of Pompeii and Herculaneum when Mount Vesuvius erupted in 79 C.E.

The bubbles in a bottle of carbonated beverage do not exist until someone removes the sealed cap, thus releasing the external pressure on the liquid. Likewise, when magma erupts from beneath the Earth's surface, the sudden release of pressure causes dissolved gases to form bubbles within the molten rock. Geologists call these bubbles "vesicles." As the bubbles grow larger, due to decreasing pressure and more gas coming out of the magma, the magma becomes less dense, so it may rise faster and spew out of the ground. Rapid cooling of the lava may solidify it into a porous, cavity-filled rock before all the bubbles have a chance to reach the surface of the liquid and burst. Pumice and scoria are two types of rock rich in vesicles. In some cases, heated groundwater may deposit other minerals such as calcite into empty vesicles after the erupted magma has solidified, so the resulting rock may resemble a cookie filled with nuts. Scientists call this texture "amygdaloidal."

Many building materials - concrete, tiles, brick, glass, paint, plaster, and drywall - contain rocks or components derived from minerals. Quarries, or open-pit mines, produce crushed rocks, gravel, and sand of different grain sizes, known as aggregates. Coarsely crushed rocks and gravel are mixed with cement, a binding material that holds the aggregate in place to form concrete. The ancient Romans invented concrete, but after their empire fell, concrete technology was forgotten until the 18th century. Limestone, a sedimentary rock, and gypsum, a mineral in sedimentary deposits, are two key ingredients of cement. Sand and smaller particles of crushed rock go into making bricks. Finely ground gypsum is filler in paint, plaster, and drywall. While different types of glass used in buildings may have specialized ingredients and coatings, they are all mostly silica, or melted quartz sand.