Arkosic Sandstone

This sandstone from southern Nevada is part of the sediment veneer that covers the ancient metamorphic schists of the craton. The near-shore sandstone was in turn overlain by deeper-water limestone as a shallow sea encroached.

Banded Iron Formation

The layers of red chert and gray, iron-rich hematite record seasonal changes in ocean waters. The iron oxide precipitated when warm, oxygen-bearing water from the surface mixed with cold, iron-rich water beneath it.

Bauxite

Bauxite, with gibbsite, boehmite, and diaspore. Aluminum is far more easily and cheaply extracted from bauxite than from granite.

Calcareous and Siliceous Ooze

Although deep-sea ooze looks like clay, a microscope photo reveals that it is made mostly of shells of tiny marine organisms, including foraminifera (calcium carbonate) and radiolaria (silica). The shells record short- and long-term changes in Earth's climate. Hole 884E: 145-884E-2W-2

Cast of Mesosaurus

Fossils of Mesosaurus, a small reptile that swam in shallow coastal waters about 275 million years ago but could not have crossed an ocean, occur in both South America and Africa.

Cave Popcorn

Formed on cave walls, the sides of other formations, and at the edges of pools.

Coconino Sandstone

Compare this sandstone with its layers intact with specimen 76943---the same stone but with crushed and melted sand grains from a meteor impact.

Crushed Stone and Gravel

Crushed rock (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.

Dolomitic Limestone

The North American craton was periodically flooded by shallow seas that left behind widespread layers of sediment, which formed a veneer of sedimentary rocks like this dolomitic limestone.

Flowstone

This special type of flowstone called drapery was deposited by water flowing down a cave wall.

Glossopteris

Fossils of the land plant Glossopteris, all roughly 300 million years old, are found in Africa, South America, Australia, India, and Antarctica.

Glossopteris

Fossils of the land plant Glossopteris, all roughly 300 million years old, are found in Africa, South America, Australia, India, and Antarctica.

Impact Breccia

Impact Breccia

These jumbles of glass and crushed rock are impact breccias. The dark, flattened and twisted fragments in the Ries breccia slab are pieces of impact glass. In samples from older craters such as Gosses Bluff, similar glass pieces have weathered to clay.

Limestone

Limestone, faulted into blocks. Movement in a fault zone chopped this layered rock into pieces, which tilted like books on a shelf.

Limestone with ammonites

Psiloceras planoribis, Lower Jurassic period. What time is it? If you found this index fossil in a rock, you'd know. The animal was once widespread but quickly became extinct. Only a small percentage of fossils meet these criteria.

Lunar Regolith Breccia 15459

This regolith breccia includes fragments of dark mare basalt from a lava-filled basin and lighter anorthosite from the highlands. Collected by Apollo 15.

Mesosaurus

Fossils of Mesosaurus, a small reptile that swam in shallow coastal waters about 275 million years ago but could not have crossed an ocean, occur in both South America and Africa.

Native Copper-bearing Conglomerate

As North America's rift failed, sulfur-poor solutions percolated through its rocks, taking copper from basalt and depositing it in overlying sediments.

Polymict Breccia 67915

Generations of impacts shattered and melted the Moon's crust, welding together new rocks called breccias. In this sample, even the small fragments are composed of still smaller bits of rock. Collected by Apollo 16.

Sandstone

Contains 1.6% water by weight. Water volume: 126 milliliters.

Sandstone

Sandstone faulted during compaction.

Sandstone

A meteorite struck the Earth. Within seconds, the impact sent out a shock wave that created cone-shaped fractures, called shattercones. Their tips originally pointed to the impact site.

Sandstone

Coconino Sandstone. A small four-legged animal walked across a sand dune 265 million years ago, leaving behind its foot- and claw-prints. Before the tracks were erased, another sand layer covered and preserved them.

Sandstone

Marine animals--probably trilobites--scratched out furrows in the mud 500 million years ago. Sand filled in the furrows, and both eventually turned to rock. Cambrian Period.

Sandstone

Fountain Formation, Pennsylvanian Period. Sandstone is a sedimentary rock--one that formed from sediments deposited at Earth's surface by water, ice, or wind. The sand and pebbles that make up this sandstone are fragments from older rocks. The fragments were carried downhill by rivers and streams 300 million years ago, deposited in layers, then bound together by natural cement.

Sandstone

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

Sandstone baluster from Capitol

This weathered baluster once adorned the Capitol's East Front. Even layers of white paint couldn't keep parts of its surface from weathering away in layers, like those of an onion.

Sandstone baluster from White House

The base of this sandstone baluster is missing its edges. They broke off along the layers under the weight of the sandstone itself and the stone railing the baluster supported. The circular marks were made by a saw when the piece was removed.

Sandstone brackets from Capitol

Carved brackets, Cretaceous Period. These two carved brackets were nearly identical when installed in the 1790s. Over the next 160 years, many layers of paint were applied to protect the easily weathered sandstone. The one with more paint retains more of the original detail.

Sandstone from White House

Potomac Formation. A microscope photo of the sandstone reveals that it contains too much clay to be very durable. It also has other flaws (not visible here) that can cause big problems for a building stone: isolated large pebbles and clay lumps, and uncemented areas.

Sandstone lintel from White House

Lintel with concrete patch.

Sandstone with gastropods

Turritella mortoni, Paleocene Epoch. What time is it? If you found this index fossil in a rock, you’d know. The animal was once widespread but quickly became extinct. Only a small percentage of fossils meet these criteria.

Shale

Raindrops gently splattered pits into fine-grained sediment some 215 million years ago. Before the next storm erased the impressions, more sediment covered and preserved them.

Shale with graptolites

Tetragraptus approximatis, Ordovician Period. What time is it? If you found one this index fossil in a rock, you'd know. Each animal was once widespread but quickly became extinct. Only a small percentage of fossils meet these criteria.

Shocked Coconino Sandstone

Look for the crushed and melted sand grains and no visible layers, shocked by a meteor impact. Look at sandstone 6812 to see what it looked like before.

Stalactite

An icicle-shaped formation that grew down from a cave roof. Early in their growth, stalactites resemble soda straws.

Stalagmite

A pillar-shaped formation that grew up from a cave floor. The drip and flow of water, along with the varying rate of growth, produced this specimen's texture.

Witwatersrand Conglomerate

This rock contains tiny sedimentary particles of gold, uraninite, and pyrite. Such ores can no longer form. Higher levels of oxygen in today's atmosphere would alter the uraninite and pyrite particles before they could be deposited.