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TITLE: A City Made of Rock

Like all cities, Washington, D.C. is made of rocks and rock products. Marble, sandstone, and granite can be cut, shaped, and polished to cover buildings. Concrete, crushed stone, and asphalt are all building materials humans produce from minerals, rocks, or petroleum. Construction materials such as brick, tile, plaster, wallboard, and steel are also made with rock-derived ingredients. Even the glass in windows is made with finely ground and melted sand.

[Photo: Sandstone]

Beach sand may one day harden into rock like this. The Smithsonian Castle is made of a red sandstone from Poolesville, Maryland.

[Photo: Granite]

This familiar rock makes objects that take great wear and tear. That’s why many road and railroad beds, curbstones, cobblestones, monuments, statues, and tombstones are made of granite.

[Photo: Marble]

This marble was once limestone. It was transformed by heat and pressure within the Earth.

[Photo: Concrete]

The ancient Egyptians, Greeks, and Romans all used concrete, a synthetic rock. Heating limestone, clay, and silica to 1,425 C (2,600 F) makes cement, the glue in concrete. Combining cement, aggregate (crushed stone, or sand and gravel), and water forms concrete.

[Photo: Asphalt]

Asphalt is a tarlike hydrocarbon mixture that is solid or semisolid at room temperature. It is heated and combined with aggregate (crushed stone, or sand and gravel) to form the familiar material that paves most roads. Most asphalt is made by evaporating crude oil.

[Photo: Gravel]

Gravel and Crushed Stone
Crushed stone (mainly limestone and granite), sand, and gravel are so essential to urban life that billions of dollars worth are produced each year. They’re used in concrete, roads, and virtually all construction sites. Sand and gravel cover the paths of the National Mall.

[Photo: Arial view of U.S. Capital and buildings to the south.]


Smithsonian National Museum of Natural History