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| Aphanitic.jpg Hand sample showing aphanitic (fine-grained) igneous texture which is characterized by individual crystals too small to be indentified by the unaided eye. Fine grained texture indicates rapid cooling in a surface, or near surface environment. | AphaniticPM.jpg Photomicrograph of aphanitic (fine-grained) igneous texture. |
| Phaneritic.jpg Hand sample showing phaneritic (coarse-grained) igneous texture. Phaneritic rocks form when large masses of magma solidify slowly at depth generating crystals large enough to identify without the aid of a microscope. | PhaneriticPM.jpg Photomicrograph of phaneritic (coarse-grained) igneous texture. |
| Porphyritic.jpg Hand sample showing porphyritic igneous texture. The large crystals are referred to as phenocrysts whereas the matrix of smaller crystals is called groundmass. Porphyritic rocks have a complex cooling history. | PorphyriticPM.jpg Photomicrograph of porphyritic igneous texture. |
| Glassy.jpg Hand sample showing glassy igneous texture. Glassy rocks are the result of rapid cooling, or form when very viscous magma solidifies. | GlassyPM.jpg Photomicrograph of glassy igneous texture. |
| Vesicular.jpg Hand sampling showing vesicular igneous texture. Vesicular rocks contain voids left by gas bubbles that escaped as lava solidified. | Pyroclastic.jpg Hand sample showing pyroclastic (fragmental) igneous texture. Pyroclastic rocks form from rock fragments that are ejected during violent volcanic eruptions. |
| Pegmatitic.jpg Outcrop showing pegmatitic igneous texture characterized by unusually large crystals. Pegmatites form in the late stages of crystallization, where ion migration is enhanced by fluids and results in the growth of especially large crystals. | Granite.jpg Hand sample of the intrusive igneous rock granite, one of the most common rocks of the upper continental crust. |
| GraniteCU.jpg Close up of the igneous rock granite. | Granite Porphyry.jpg Hand sample of igneous rock granite porphyry. |
| Granite PorphyryCU.jpg Close up of igneous rock granite porphyry. | Half Dome.jpg Half Dome, a granite monolith in Yosemite National Park, California. |
| Rhyolite.jpg Hand sample of the extrusive igneous rock rhyolite. Rhyolite is a fine-grained igneous rock with the same mineral composition as granite. | RhyoliteCU.jpg Close up of the igneous rock rhyolite. |
| Obsidian.jpg Hand sample of the glassy igneous rock obsidian. | Obsidianflow.jpg Obsidian flow that was extruded from Newberry Caldera, Oregon. |
| Lava Dome.jpg The face of this lava dome, located south of Mono Lake, California, is composed of the glassy, igneous rock obsidian. | Pumice.jpg Hand sample of the igneous rock pumice. Some samples of pumice contain so many voids that they float. |
| Deposits.jpg Pumice deposits near Crater Lake, Oregon. | Pumice Andesite.jpg Hand sample of the extrusive igneous rock andesite. Andesite is named for the Andes Mountains, where numerous volcanoes are composed of this rock type. |
| Andesite Porphyry.jpg Hand sample of igneous rock andesite porphyry. | Andesite PorphyryCU.jpg Close up of andesite porphyry illustrating its porphyritic texture. |
| Lassen Peak.jpg Lassen Peak, California, a volcano in the Cascade Range that is composed mainly of andesite. Lassen Peak last erupted explosively in 1917. | Diorite.jpg Hand sample of the intrusive igneous rock diorite. |
| DioriteCU.jpg Close up of the igneous rock diorite. | Basalt.jpg Hand sample of the igneous rock basalt. |
| BasaltCU.jpg Close up of the igneous rock basalt, the most common extrusive igneous rock. Many volcanic islands and the upper layer of the oceanic crust are composed of basalt. | Fluid Basalt.jpg Fluid basalt flow erupting from Hawaii's Kilauea Volcano. |
| Layers of Basalt.jpg Layer upon layer of basalts that form the Columbia Plateau region of the northwestern United States. | Basalt Sill.jpg The reddish-black horizontal layer in the middle of the photo is a basalt sill, Salt River Canyon, Arizona. |
| Scoria.jpg Hand sample of the vesicular igneous rock scoria. | Gabbro.jpg Hand sample of the igneous rock gabbro. |
| GabbroCU.jpg Close up of the igneous rock gabbro. | Tuff.jpg Outcrop of welded tuff, an igneous rock composed of tiny glass shards that contains walnut-sized pieces of pumice and other rock fragments. |
| Porphyritic Texture.jpg Hand sample of porphyritic igneous texture having feldspar phenocrysts and a fine grained groundmass. | Basalt Dike.jpg Basalt dike cutting through metamorphic rock. |
| ColumnarJointing.jpg Igneous rocks exhibiting columnar jointing Devils Tower, Wyoming. | Shale.jpg Hand sample of the sedimentary rock shale. |
| Sandstone.jpg Hand sample of the sedimentary rock sandstone. | Quartz Sandstone.jpg Close up of a quartz sandstone. |
| Navajo Sandstone.jpg Thick layer of sandstone (called the Navajo Sandstone) exposed near Zion National Park, Utah. | Sand Dunes.jpg Sand dunes composed of well sorted quartz grains illustrating the environment in which the Navajo Sandstone formed. |
| Conglomerate.jpg Hand sample of the sedimentary rock conglomerate. | ConglomerateCU.jpg Close up of the sedimentary rock conglomerate. |
| Conglomerate Layers.jpg Outcrop showing interbedded, conglomerate and sandstone layers. | Breccia.jpg Hand sample of the sedimentary rock breccia. |
| BrecciaCU.jpg Close up of the sedimentary rock breccia. | Limestone.jpg Hand sample of the sedimentary rock limestone. This compact form of limestone, sometimes called lithographic limestone, is formed by chemical precipitation. |
| Kaibab Limestone.jpg Outcrop of limestone capping the South Rim of the Grand Canyon called the Kaibab Limestone (uppermost layer). | Fossiliferous Limestone.jpg Hand sample of fossiliferous limestone, a sedimentary rock having a biochemical origin. |
| Fossil Corals.jpg Hand sample of fossil corals. These organisms are capable of creating large quantities of marine limestone. | Limestone Cliffs.jpg Massive limestone cliffs of El Capitan Peak, Texas once a portion of a large coral reef. |
| Travertine.jpg Cut slab of travertine, a type of inorganic limestone commonly found decorating caves. Note the somewhat concentric layers. | Travertine Cave.jpg Travertine exposed in a cave. |
| Coquina.jpg Hand sample of the sedimentary rock coquina, composed almost entirely of sea shells. | CoquinaCU.jpg Close up of the sedimentary rock coquina. |
| Chalk.jpg Hand sample of the sedimentary rock chalk. | Chalk Deposits.jpg Prominent chalk deposits of the White Cliffs of Dover, England. |
| Chert.jpg Samples of the sedimentary rock chert. Chert is a hard rock made of microcrystalline silica which was shaped into tools by Native Americans. | Flint.jpg Flint, a dark form of chert, whose colour results from the organic matter it contains. |
| Agate.jpg Agate, a banded form of chert. | Jasper.jpg Jasper, a red variety of chert gets its coloration from iron oxide. |
| Rocksalt.jpg Hand sample of rock salt, a sedimentary rock formed by evaporation and used as common table salt. | RocksaltCU.jpg Close up of rock salt. |
| Gypsum.jpg Hand samples of gypsum, also called rock gypsum. Rock gypsum forms when sea water evaporates. It is used for plaster and wallboard. | Salt Flats.jpg View of salt flats in the western United States. |
| Peat.jpg Hand sample of peat, a partially altered plant material that is the source material for coal. | Lignite.jpg Hand sample of lignite, a sedimentary rock mined as soft coal that produces moderatre amounts of energy. |
| Bituminous.jpg Hand sample of bituminous, a major form of coal that has a high energy output. | Anthracite.jpg Hand sample of anthracite, the metamorphic form of coal. |
| Strata.jpg Outcrop showing strata or beds, the most characteristic feature of sedimentary rock. | Cross-bedding.jpg Outcrop illustrating cross-bedding that results when sediments do not accumulate in horizontal beds. |
| Mudcracks.jpg Mud cracks are features found in sedimentary rocks that indicate the sediment dried out and shrank, producing cracks. Mud cracks are associated with such environments as tidal flats and shallow lakes. | Fossils.jpg Fossils, the remains or traces of prehistoric life, are important inclusions in sedimentary rocks. Knowing the nature of the life forms helps researchers understand past environments. |
| Slaty Cleavage.jpg Outcrop showing rock or slaty cleavage, a type of foliated metamorphic texture that exhibits closely spaced planar surfaces along which rock tends to split easily. | Schistosity.jpg Hand sample showing schistosity, a foliated metamorphic texture where platy minerals give the rock a planar or layered structure. |
| Gneissic Texture.jpg Hand sample showing gnessic texture, a foliated metamorphic texture where light and dark minerals have separated giving the rock a banded appearance. | Marble.jpg This hand sample of marble contains large equidimentional crystals that exhibit a nonfoliated metamorphic texture. |
| Calcite CrystalsPM.jpg Photomicrograph using polarized light to show the interlocking calcite crystals in marble. | Mica Garnet Schist.jpg This hand sample of mica garnet schist exhibits a porphyroblastic texture, where large garnet grains are surrounded by a fine-grained matrix of other minerals. |
| Porphyroblast.jpg Close up of large garnet crystal called a porphyroblast. | Slate.jpg Hand sample of slate, a very fine-grained metamorphic rock. |
| Slate Roof.jpg Because slate breaks into flat slabs, it has many uses as a building stone as exhibited by this slate roof. | Phyllite.jpg Hand sample of the metamorphic rock phyllite. Note the characteristic glossy sheen. |
| Phyllite Glossy.jpg Comparison of phyllite (glossy) and the slate (dull). | Mica Schist.jpg Hand sample of the metamorphic rock mica schist. |
| Gneiss.jpg Hand sample of the metamorphic rock gneiss. | Metaconglomerate.jpg Close up of a metaconglomerate, also called a stretched pebble conglomerate. |
| Quartzite.jpg Hand sample of the nonfoliated metamorphic rock quartzite. | Roof Pendant.jpg Dark metamorphic rocks (roof pendant) overlie an intrusive igneous body (light colour). |
| Igneous Pluton.jpg Close up of a contact between an igneous pluton and metamorphosed host rock. | Fault Breccia.jpg Outcrop of fault breccia, consisting of angular fragments produced by movement along a fault zone. |
| Folded Gneiss.jpg Hand sample of a folded gneiss. | Metamorphosed Rocks.jpg Outcrop showing deformed and metamorphosed rocks. |
| Migmatite.jpg Outcrop of a migmatite. The lightest coloured layers are igneous, while the darker bands are metamorphic. | Vishnu Schist.jpg Outcrop of metamorphic rock called the Vishnu Schist (dark colour) intermixed with granite (pinkish colour) found at the bottom of the Grand Canyon, Arizona. |