Hailing from Glaciers, Geysers and Volcanoes, These Iconic Rocks Provide a Glimpse into How America was Formed and Built

In celebration of National Rock Day, learn how several rock specimens in the new exhibition “From These Lands” shed light on the nation’s geological heritage

Choosing the appropriate rocks and minerals for an exhibit is a multi-city process. When selecting which rocks to display in “From These Lands”, a new exhibition at the National Museum of Natural History, rocks and ores collection manager Leslie Hale shuttled between the museum in downtown Washington, D.C., and the Smithsonian’s Museum Support Center in Maryland to closely inspect hundreds of specimens. She was on the hunt for the most iconic rocks to represent each U.S. state.

“When determining if a rock is perfect for an exhibit, we consider its size, how good of an example it is and its beauty,” she said. “Is it interesting and pretty to look at? Because that’s what’s going to catch people’s eye.”

After much deliberation, collections and exhibit staff selected 43 rocks, minerals and meteorites for the exhibit, including several official state rocks and minerals. The specimens come from a diverse range of environments all over the country, including glaciers, geysers and volcanoes, and provide insights into how the land and our relationship to it have changed over time. Here are some of Hale’s favorite rocks in the exhibit.

Glacial striae (New York)

The scrapes on this rock, called striae or striations, were caused by a glacier moving across the land. The rock has two possible origins. It may be a glacial erratic, which is a rock that is picked up on the underside of a glacier, dragged along the bedrock as the glacier moves and deposited in a new location (in this case, Rochester, New York). But Hale believes that this specimen is more likely a piece of Rochester’s own bedrock that was scraped by a glacial erratic as a glacier moved across Upstate New York. This rock shows scientists that glaciers once moved across the landscape in New York, and the fact that not all the striations are parallel indicates that this particular glacier changed directions during its journey.

Scratched out words still faintly visible on the surface of this specimen — “Presented by Ward” — provide clues into its origins. The museum acquired this rock in 1886 as a transfer from the U.S. Geological Survey through Henry Ward, a geologist who sold rocks, minerals and other natural science specimens to museums. Quite a few of the Smithsonian’s early rock specimens were purchased from the company he founded, Ward’s Science, which still exists today.

Bauxite (Arkansas)

The spherical grains of varying sizes and colors that give this sedimentary rock a bubbly texture are known as pisoliths. Although it doesn’t look shiny or metallic, bauxite is the primary ore of aluminum, and most of the world’s aluminum is extracted from it. It is also the state rock of Arkansas, which was once the world’s leading resource for aluminum.

“We have a whole collection of bauxite from Arkansas, so I had a lot of choices and a really good time picking this one out,” said Hale. “I went for one that I thought was visually striking and interesting to look at.”

Before people figured out how to extract aluminum from bauxite, the metal was considered to be more valuable than gold, despite being one of the most abundant elements in the crust of the Earth. The very top of the Washington Monument is composed of solid aluminum because when the structure was completed in 1884, aluminum was still precious and difficult to extract from rock. In 1887, Austrian chemist Karl Josef Bayer developed a chemical process to extract aluminum from bauxite that is still used today.

Pahoehoe (Hawaii)

This rock was once hot, flowing lava. Pronounced pah-hoy-hoy, the word pahoehoe comes from the Hawaiian verb meaning “to paddle” and refers to a type of lava with a smooth, billowy and ropy surface. Similarly to how a rug pushed against a wall bends and ripples, lava slowly flowing and rippling led to the smooth folds seen on this igneous rock. As the outer crust of the lava cooled and hardened, lava continued to flow underneath, wrinkling the surface. The resulting rock thus records the direction the lava was flowing: perpendicular to the folds.

The United States has about 170 active volcanoes, making it the country with the most volcanoes in the world. Most of its volcanoes are located in Hawaii and Alaska. Volcanic rocks like this specimen from Hawaii resonate strongly with Hale.

“Even as a geologist, I have a hard time wrapping my head around long periods of time,” she said. “I like volcanic rocks because they form in a human lifespan or less, in a timescale that you can actually watch.”

Marble (Vermont)

The fact that this specimen’s catalog number, 17495, begins with a one indicates that it’s been in the museum’s collection since around 1880, just a few decades after the Smithsonian Institution was founded. Early geologic studies at the museum focused on rocks that made good building stones, and this marble from Vermont was probably acquired as an example of a domestic building stone, prepared the way a quarry might prepare it to research its physical properties for engineering use.

“In the early history of this country, we were still importing European building stones, but that was expensive and there was plenty of rock here,” said Hale. “So geologists started doing engineering tests on U.S. rocks to determine which made the best building stones.”

These tests likely included measuring how much weight the stone could bear before buckling and seeing if it could withstand acid rain — a test this specimen would likely fail because marble is susceptible to corrosion from acids.

Geyserite (Wyoming)

Although it isn’t shiny or colorful, this specimen is actually a type of opal — and what it lacks in luster, it makes up for in its fascinating origins. Found only on the rims of geysers, geyserite is formed over time as a geyser repeatedly erupts. As hot water rises through the ground to the surface of a geyser, it dissolves minerals from the rock it passes through. When the water shoots up and hits the colder air outside the geyser, the minerals in the water precipitate out, forming this unique deposit.

Geyserite forms in few places around the world, and this specimen was collected in Wyoming from Yellowstone National Park. The park contains more than half of the world’s active geysers, and some geysers at the park are surrounded by large, layered terraces of geyserite deposits that have accumulated.

Ashley D'Souza | Read More

Ashley D’Souza is a science writing intern at the Smithsonian’s National Museum of Natural History, where they cover natural history research and collections news for the museum’s blog, Smithsonian Voices. Ashley is currently completing their master’s degree in science writing at MIT, where they write about any and all things wildlife. They also run the blog and YouTube channel, Confessions of a Bird Freak. In their free time, Ashley can be found wandering through the woods with their camera and binoculars and talking to trees and birds. See more of Ashley’s work at https://ashleydsouza.contently.com/ and https://confessionsofabirdfreak.com/.