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Tasa Photo CD-ROM: Rock Cycle I Captions

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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.


Pumice Deposits.jpg
Pumice deposits near Crater Lake, Oregon.


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 color results from the organic matter 
it contains.

Jasper.jpg
Jasper, a red variety of chert gets its coloration from iron oxide.

Agate.jpg
Agate, a banded form of chert.

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 moderate 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 gneissic 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 color).

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 colored layers are igneous, while the 
darker bands are metamorphic.

Vishnu Schist.jpg
Outcrop of metamorphic rock called the Vishnu Schist (dark color) 
intermixed with granite (pinkish color) found at the bottom of the Grand 
Canyon, Arizona.