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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.