Teton Rocks

Geologic Map

Grand Teton National Park, Teton County, WY

Each color represents a different geologic unit; a single rock type or a group of rocks formed at the same time. A solid line represents a fault, the axis of a fold or the boundary between units.

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Teton Rocks
Metamorphic Rocks

Metamorphic rocks form from other rocks. Heat and pressure deep underground transform or metamorphose sedimentary, igneous or other metamorphic rocks into new rocks. These rocks may appear as if they were once molten, but they were more like silly putty that deformed slowly over a great length of time.

Gneiss

Site: Mt. Moran, Teewinot

Gneiss forms at high temperature and pressure deep underground. Layered gneiss has distinct layers alternating dark gray and white. These layers form during metamorphism and are not the original rock layers.

"Bright-eyed" Gneiss

Biotite mica provides the dark gray background. Small magnetite crystals, rich in iron, form the “eyes” surrounded by bleached zones with no biotite. Search for this rock along the Death Canyon trail.

Amphibolite

Amphibolite forms at moderate temperatures and pressures of the minerals hornblende and plagioclase. Hornblende is dark green to almost black and glints in the sun. Plagioclase is white giving a speckled look.

Quartzite

Amphibolite forms at moderate temperatures and pressures of the minerals hornblende and plagioclase. Hornblende is dark green to almost black and glints in the sun. Plagioclase is white giving a speckled look.

Steatite

Steatite is also known as soapstone because of the rock’s slippery feel. It is composed mostly of talc, the Earth’s softest mineral, and is very easily carved. American Indians carved bowls from steatite.

Teton Rocks
Igneous Rocks

Igneous rocks crystallize from magma originating in the Earth’s crust or mantle. The magma cools and crystallizes to form many common rocks like granite and basalt. The magma may erupt to form volcanic rocks, or cool underground to form intrusive rocks.

Granite

Silica-rich magma crystallizes underground to form granite. The rock is white or sometimes pink speckled with black mica and lacks layers. Granite is the hardest rock in the park forming the highest peaks.

Pegmatite

Silica-rich magma squeezes into cracks in the bedrock and crystallizes slowly to form pegmatite. The chemical composition is the same as granite, but the crystals are larger because they grow more slowly.

Diabase

Basaltic-magma with less silica than granite crystallizes underground instead of erupting to form diabase. Look for narrow vertical black dikes transecting the faces of Mount Moran and the Middle Teton.

Obsidian

Obsidian is black volcanic glass. If silica-rich magma cools very fast, crystals do not grow and glass forms. American Indians sought obsidian in Yellowstone and on Teton Pass to flake into projectile points.

Teton Rocks
Sedimentary Rocks

Sedimentary rocks form at or near the Earth’s surface from weathered bits of rocks or from chemical precipitation. Layers of sediment deposited in water or on land become buried and compressed into rocks such as sandstone. Water may evaporate and precipitate compounds that form chemical rocks such as limestone.

Shale

Burial compacts mud composed of clay, organic material and rock fragments into shale. Shale is soft and usually black to dark gray in color. It forms slopes between cliffs of more resistant sedimentary rocks.

Limestone

Limestone is both a rock formed of fossils such as shells and corals and a chemical precipitate of calcium carbonate. Light to dark gray in color, it forms sedimentary cliffs like the Death Canyon Shelf.

Conglomerate

Conglomerate is a rock made of rounded pieces of older rocks cemented together with sandstone. The quartzite cobbles covering the valley floor likely eroded out from conglomerates found northeast of the park.

Map

Meta- Morphic Rocks

Gneiss

"Bright-eyed" Gneiss

Amphibolite

Quartzite

Steatite

Igneous Rocks

Granite

Pegmatite

Diabase

Obsidian

Sedi- Mentary Rocks

Shale

Limestone

Conglomerate

Geologic Map

Teton Rocks
Metamorphic Rocks

Gneiss

"Bright-eyed" Gneiss

Amphibolite

Quartzite

Steatite

Teton Rocks
Igneous Rocks

Granite

Pegmatite

Diabase

Obsidian

Teton Rocks
Sedimentary Rocks

Shale

Limestone

Conglomerate

Teton Rocks

Geologic Map

Teton RocksMetamorphic Rocks

Gneiss

"Bright-eyed" Gneiss

Amphibolite

Quartzite

Steatite

Teton RocksIgneous Rocks

Granite

Pegmatite

Diabase

Obsidian

Teton RocksSedimentary Rocks

Shale

Limestone

Conglomerate

Teton Rocks
Metamorphic Rocks

Teton Rocks
Igneous Rocks

Teton Rocks
Sedimentary Rocks