Rock Picture Index

Master Guide to Rock Pictures and Descriptions

Cloe-up view of woman stacking pebbles, at beach
Ascent Xmedia/ Taxi/ getty Images

Refer to the following links for images of each type of rock. You may also want to use the Rock Type Identification Key.

Both documents require you to determine whether your rock is igneous, sedimentary or metamorphic. The Rock Type Identification Key has a brief list of tips for that purpose beneath the tables.


(About Igneous Rocks)

Aa—Jagged form of basalt lava.
Andesite—The typical intermediate-silica arc lava.
Anorthosite—Plutonic rock of straight plagioclase feldspar.
Basalt—Low-silica lava, the most common volcanic rock. (Picture Gallery)
Diorite—Plutonic rock between granite and gabbro.
Dunite—Plutonic rock made of straight olivine.
Felsite—Volcanic rock of the same composition as granite.
Gabbro—Coarse-grained plutonic version of basalt.
Granite—Familiar three-mineral rock essential to continents. (Picture Gallery)
Granodiorite—Plutonic rock between diorite and granite.
Komatiite—Rare and ancient ultramafic lava.
Lapillistone—Volcanic rock formed of little ash balls.
Latite—Dark, low-quartz lava, extrusive version of monzonite.
Obsidian—High-silica volcanic glass. (Picture Gallery)
Pahoehoe—Smooth-skinned flows of basalt lava.
Pegmatite—Igneous rock with very large crystals.
Peridotite—Dark, dense rock from the Earth's mantle. (Picture Gallery)
Perlite—Hydrous, lightweight obsidian or rhyolite.
Porphyry—Any igneous rock with large mineral crystals in a fine matrix.
Pumice—Light-colored, frothy high-silica lava.
Pyroxenite—Uncommon ultramafic rock from the deep sea crust.
Quartz Monzonite—Much like granite, except short on quartz.
Rhyolite—High-silica white or red lava.
Scoria—Dark, frothy low-silica lava.
Syenite—Plutonic, alkalic granitic rock without quartz.
Tonalite—Plutonic, felsic granitic rock without alkali feldspar.
Troctolite—Gabbro without pyroxene.
Tuff—Rock made from volcanic ash.

Special Galleries: Igneous Rock Classification Diagrams, Igneous Rock Textures, Ophiolitic Rocks, Phenocrysts, Pillow Lavas, Volcanic Rocks


(About Sedimentary Rocks)

Agate—Semiprecious chert of infinite variety.
Alabaster—White gypsum stone long prized for sculpture.
Arkose—Raw sandstone made from eroded granite.
Asphalt—Natural tar from petroleum seeps.
Banded Iron Formation—Extremely ancient "tiger iron."
Bauxite—Highly leached surface rock and ore of aluminum.
Breccia—Rock made from broken rocks.
Chert—Common silica-rich rock type with much variety. (Picture Gallery)
Claystone—Just what it sounds like.
Coal—The original fossil fuel.
Conglomerate—Rocks made with extra-big grains. (Picture Gallery)
Coquina—Limestone composed of shell fragments. (Picture Gallery)
Diamictite—Rock made of poorly sorted land sediment.
Diatomite—Rock made of microscopic plankton shells.
Dolomite—Carbonate rock, a near-twin of limestone.
Graywacke—Impure sandstone, also called wacke.
Gypsum Rock—Soft rock formed early in evaporating waters.
Limestone—Rock composed of calcite, Earth's greatest store of carbon. (Picture Gallery)
Peat—Brown, vegetative precursor to coal.
Porcellanite—An earthy looking sub-chert.
Rock Salt—Massive halite, the only edible stone.
Sandstone—Where sand goes to and comes from.
Shale—Thin-layered rock made from mud and clay.
Siltstone—Made from sediment finer than sand.
Travertine—Type of limestone precipitated in springs. (Picture Gallery)

Special Galleries: More Sedimentary Rocks, Sedimentary Rock Classification Diagrams, Sedimentary Structures, Sedimentary Textures


(About Metamorphic Rocks)

Amphibolite—High-grade rock, typically a hornblende schist.
Argillite—Low-grade rock, formerly claystone.
Blueschist—Rock made by high-grade metamorphism in subduction zones.
Cataclasite—Ground-up rock found in fault zones.
Eclogite—The most extreme metamorphic rock you can find. (Picture Gallery)
Gneiss—Banded and tough, it forms the lower crust.
Greenschist—Rock made by low-grade metamorphism of various rock types.
Greenstone—Dark rock made by metamorphism of basalt.
Hornfels—Tough and fine-grained, it forms where igneous rocks cook it.
Marble—Coarse-grained, metamorphosed limestone.
Migmatite—Swirly-banded rock produced by extreme metamorphism.
Mylonite—Milled and melted rock from deep in fault zones.
Phyllite—Shiny, colorful metamorphosed slate. (Picture Gallery)
Quartzite—Rugged metamorphosed sandstone.
Schist—Finely striped rock made by metamorphism of mudstones.
Serpentinite—Green, scaly metamorphosed ocean crust. (Picture Gallery)
Slate—Platy rock made by mild metamorphism of shale. (Picture Gallery)
Soapstone—Soft and carvable, hydrothermally altered lava.

Special Galleries: Hydrothermal Features, Metamorphic Fabrics, More Metamorphic Rocks, Porphyroblasts


Artificial Rocks Gallery—Brick, concrete, and other geotechnical products.
Concretions Gallery—Odd sedimentary lumps​, often mistaken for fossils.
Fulgurite Gallery—Lightning striking the ground makes these curious objects.
Geode Gallery—Sedimentary features with hollow, glittering interiors.
Meteorite Gallery—Various stones from interplanetary space.
Official State Rocks of the United States—Twenty-five states have one.
Pet Rocks—Favorite stones from me and other contributors.
Thunder Egg—Solid, agate-filled lump found in certain volcanic lands.