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Aa Lava

Aa Lava

Aa (ah-ah) lava is cooler and slower-moving; it breaks into jagged chunks.

Andesite Lava

Andesite Lava

The black crystals in this specimen are the water-bearing minerals amphibole and biotite: evidence of the magma's high water content. The abundant large white crystals of plagioclase helped make the magma highly viscous.

Andesite Lava

Andesite Lava

The black crystals in this specimen are the water-bearing minerals amphibole and biotite: evidence of the magma's high water content. The abundant large white crystals of plagioclase helped make the magma highly viscous.

Banded Pumice

Banded Pumice

Like most pumices from the Lassen Peak eruption, this one is banded. The light- and dark-colored bands represent two chemically distinct types of magma that mingled during the eruption.

Basalt

Basalt

The most common rock of oceanic crust, basalt erupts on the sea floor at spreading ridges.

Basalt

Basalt

Sunset Crater. The presence of green olivine crystals in a glassy matrix is one clue to this rock's origin. Another is its rough, spongy appearance--the result of gas escaping during eruption.

Basalt

Basalt

Erupted 1943-1947. The basalt is made up of brown glass and the mineral olivine. As it erupted and cooled, escaping gas bubbles created its spongelike texture.

Basalt (Volcanic bomb)

Basalt (Volcanic bomb)

Basalt erupted in 1975-1976. A volcano spit out this clot of magma, which then twisted, cooled, and solidified during its half-minute descent. Escaping gases produced the spongy texture.

Basalt Drill Core

Basalt Drill Core

Depth 48.3 meters; Drill Hole 79-1 erupted 1959, sampled 1979. This sample, which was relatively close to the lake's surface, had completely crystallized by 1979.

Basalt Drill Core

Basalt Drill Core

Depth 51.9 meters; Drill Hole 79-1 erupted 1959, sampled 1979. At this depth, the lava still contained 18 percent liquid (now brown glass) in 1979.

Basalt Drill Core

Basalt Drill Core

Depth 53.1 meters: Drill Hole 79-1 erupted, 1959, sampled 1979. Deeper and hotter, the lava was 24 percent liquid (now brown glass) in 1979.

Basalt Drill Core

Basalt Drill Core

Depth 55.6 meters; Drill Hole 79-1; erupted 1959, sampled, 1979. Deep within the lake the lava was 31 percent liquid (now brown glass) in 1979. Notice that the black iron-titanium oxide minerals visible in the other drill core photos had not yet started to crystalize.

Basaltic Cinders

Basaltic Cinders

We reassembled these layered cinders as they appeared at Dotsero Volcano, a cinder cone in western Colorado. Like many cinder cones, Dotsero is quarried for construction material.

Basaltic Dike

Basaltic Dike

At spreading ridges on the sea floor, new basaltic material wells up in cracks through earlier solid basalt. This glassy basaltic dike was injected into solid basalt, shouldering it aside and forcing the two tectonic plates to move apart. Hole 504B: 111-504B-142R-01A. 9-17 cm, #1B

Basaltic Lava

Basaltic Lava

This sample came from a road cut in central Washington, more than 160 km (100 mi) from the fissures where it erupted. The scattered holes were left by gas bubbles in the lava when it solidified.

Breadcrust Block

Breadcrust Block

This block was still hot when it rolled down the growing lava dome. The surface cooled and solidified, but hot gases expanded inside until the crust cracked. Baking bread cracks the same way: hence the name, breadcrust block.

Breadcrust Block

Breadcrust Block

This dacite block tumbled from the growing lava dome in Mount St. Helens's crater. After the crust hardened, gas continued to expand in the partly molten interior, swelling and cracking its surface like bread when it bakes.

Cut Pillow Lava

Cut Pillow Lava

The outer rind of this pillow lava cooled so quickly as it came in contact with cold seawater that it formed a clear brown glass. The interior cooled more slowly, and clusters of dark crystals grew around preexisting minerals.

Dacite

Dacite

This is a small piece of a dump truck-sized lava block. It was carried down the volcano's flanks by a roiling mudflow on May 19, 1915. Days after such blocks came to rest, many were still too hot to touch.

Dacite

Dacite

This is a small piece of a dump truck-sized lava block. It was carried down the volcano's flanks by a roiling mudflow on May 19, 1915. Days after such blocks came to rest, many were still too hot to touch.

Diabase

Diabase

Belmont Diabase Sheet. The large black pyroxene and white plagioclase crystals--and the absence of glass or gas cavities--are giveaways that this rock cooled slowly underground.

Distant Volcanic Ash

Distant Volcanic Ash

Just three hours after the eruption began, fine ash started to fall on Spokane, Washington, 390 km (240 mi) northeast of the volcano. A dusting of ash was noticed as far as 1,500 km (930 mi) to the east.

Dunite in Basaltic Lava

Dunite in Basaltic Lava

This slab of black basalt contains rounded xenoliths of dunite, a rock composed entirely of green olivine crystals. Dunite accumulates in the deep interiors of Hawaiian volcanoes. Vigorous eruptions bring fragments to the surface.

Fulgurite in andesite

Fulgurite in andesite

Fulgurite, in weathered andesite. Lightning hit a volcano, instantly melting the rock to create this fulgurite. The liquid cooled too quickly for crystals to form. Hollow tubes lined with greenish-black glass record the electric current's path through the rock.

Gabbro

Gabbro

Much of the magma that feeds spreading ridges stagnates near the base of the oceanic crust, where it crystallizes to form the coarse-grained rock called gabbro. The large, interlocking crystals are evidence that it cooled slowly. Hole 735B: 118-735B-74R-07. 128-135 cm, #1F

Glassy basalt

Glassy basalt

Glassy Basalt formed into souvenir medallions while still molten.

Glassy basalt

Glassy basalt

Glassy Basalt formed into souvenir medallions while still molten.

Glassy basalt

Glassy basalt

Glassy Basalt formed into souvenir medallions while still molten.

Granite

Granite

Pikes Peak Granite

Granite

Granite

Granite, Ordovician Period. This familiar city rock beautifies buildings and 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.

Granite

Granite

A bright green-and-orange granite, unakite, accents the Mall-side stairs of the Natural History Museum.

Granite

Granite

The most common rock of continental crust, granite is generated mainly where one plate descends below another. Water released from the descending plate triggers a complex melting sequence that ultimately yields granite.

Granite

Granite

Pikes Peak Granite, 1.03 billion years old. Granite is an igneous rock--one that solidified from a hot, molten state. The crystals in this granite formed when molten rock cooled underground 1.1 billion years ago. They grew until they bumped into neighboring crystals. As the granite slowly cooled, the crystals grew fairly large.

Granite

Granite

Conway Granite, 181 million years old.

Granite

Granite

Several varieties of granite were used in the construction of this building. This rock, a variety of granite called unakite, is about 1 billion years old, and was used to trim the museum's front steps.

Granite

Granite

Sebago Granite. You can tell by the mosaic of interlocking crystals--gray quartz, pink and white feldspar, black biotite, and silvery muscovite--that this rock is Plutonic.

Granite

Granite

Contains 0.8% water by weight. Water volume:79 milliliters.

Granite

Granite

Several varieties of granite were used in the construction of this building. This rock is 380 million years old, and was used to face and trim the museum's main building and wings.

Granite

Granite

Several varieties of granite were used in the construction of this building, because it is both durable and beautiful. This rock is 356 million years old, and was used to face the museum's main building.

Granite

Granite

Several varieties of granite were used in the construction of this building, because it is both durable and beautiful. This rock is 590 million years old, and was used to face and trim the museum's front steps and decorative accents.

Granodiorite

Granodiorite

Cathedral Peak Granodiorite.

Harzburgite

Harzburgite

Rising basaltic magma leaves behind the dense mantle rock called harzburgite. When minerals in harzburgite are replaced by less-dense serpentine, large masses of this altered rock may ascend to within reach of the drill. Hole 395: 45-395-18-1, 82-100 cm.

Kimberlite

Kimberlite

This core contains dark crustal rocks and pale green mantle rocks with red garnets.

Komatiite

Komatiite

Most komatiites formed prior to 2.5 billion years ago. Lavas rich in magnesium, they reflect unusually high eruption temperatures on the young Earth's surface. The long, dark green crystals are amphibole that replaced pyroxene.

Lamproite

Lamproite

Drab lamproite hosts the sparkling diamonds in the world's richest diamond deposit. The Argyle diamond district in Australia produces six carats of diamond per ton of ore.

Lunar Ferroan Anorthosite 60025

Lunar Ferroan Anorthosite 60025

At 4.5 billion years old, this anorthosite is approximately the same age as the Moon itself. Made mostly of plagioclase feldspar, it is thought to be a sample of the Moon\'s early feldspar crust. Collected by Apollo 16.

Lunar Olivine Basalt 15555

Lunar Olivine Basalt 15555

Mare basalts from the Imbrium Basin range from 3.2 to 3.4 billion years in age, showing that volcanism in the basin lasted over 200 million years. This specimen formed midway through the epoch. Collected by Apollo 15.

Merensky Reef Platinum Ore

Merensky Reef Platinum Ore

A spectacular and unique ore deposit, the Merensky Reef is a 5.5-m (18-ft) thick layer in a gigantic, 2.1-billion-year-old igneous complex. It contains more than half of the world’s known platinum reserves.

Nearby Pumice

Nearby Pumice

Immediately after the May 18, 1980, eruption, a hail storm of coarse pumice and rock fragments fell from the eruption cloud, blanketing the area near the volcano.

Non-welded Rhyolite Tuff

Non-welded Rhyolite Tuff

In the upper levels of the Bishop Tuff, pressure was low. Pumice and ash cooled quickly, retaining their original shapes.

Pahoehoe Lava

Pahoehoe Lava

This twisted, ropy surface is typical of pahoehoe (pa HOY hoy), a form of basaltic lava. As fluid lava flowed downhill, a thin skin on top cooled and solidified. It was wrinkled by continued movement of the molten interior.

Pahoehoe Lava

Pahoehoe Lava

This twisted, ropy surface is typical of pahoehoe (pa HOY hoy), a form of basaltic lava. As fluid lava flowed downhill, a thin skin on top cooled and solidified. It was wrinkled by continued movement of the molten interior.

Pahoehoe Lava

Pahoehoe Lava

A geologist's hammer was singed when used to collect molten pahoehoe lava, which dripped down before freezing in the air.

Pele's Hair and Pele's Tears

Pele's Hair and Pele's Tears

Pele's hair forms when wind draws droplets of liquid basalt into strands, like cotton candy. Droplets that break off are called Pele's tears.

Pillow Basalt

Pillow Basalt

This pillow basalt erupted and cooled quickly on the sea floor. Hole 504B: 69-504B-4-4. 0-10 cm, #327

Pillow Lava

Pillow Lava

Toothpaste squeezed from a giant tube? No, this is a pillow of basalt, the most common lava erupted on the sea floor. Its thin coating of dark manganese oxide minerals was precipitated from hot mineral-rich water, perhaps with the aid of bacteria.

Pseudotachylite with Granite Fragments

Pseudotachylite with Granite Fragments

This specimen comes from an ancient impact crater at least 300 km (185 mi) across. The black rock, pseudotachylite, formed when friction along fractures melted the rock. The pink and white fragments are the original granite.

Rhyolite

Rhyolite

Glass Creek Dome, erupted 600 years ago.

Slightly Welded Rhyolite Tuff

Slightly Welded Rhyolite Tuff

In the last 2.1 million years, three enormous eruptions have occurred in and near Yellowstone National Park. Each produced huge flows of hot debris that came to rest to form hard volcanic rocks like this tuff.

Slightly Welded Rhyolite Tuff

Slightly Welded Rhyolite Tuff

In the last 2.1 million years, three enormous eruptions have occurred in and near Yellowstone National Park. Each produced huge flows of hot debris that came to rest to form hard volcanic rocks like this tuff.

Spindle Bomb

Spindle Bomb

Cinder cone eruptions launch clots of basaltic magma into the air, where they may solidify into contorted shapes before falling to Earth. This Paricutín bomb originally had tapered tails on both ends.

Strongly Welded Rhyolite Tuff

Strongly Welded Rhyolite Tuff

Each of Yellowstone's three major eruptions produced huge flows of hot debris that formed thick hot deposits. The deposit interiors were hot enough to compress, squeezing once-rounded pumices into flattened disks, such as in this strongly welded tuff.

Volcanic Bomb

Volcanic Bomb

This volcanic bomb was ejected from Heimaey as a clot of molten basalt. It flattened on impact, producing a turtle-shell shape. The surface cooled quickly, forming a flaky skin.

Welded Rhyolite Tuff

Welded Rhyolite Tuff

The thin, dark streaks in this specimen were once rounded pumice lumps. Pressure and heat deep within the Bishop Tuff welded pumice and ash together.


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