INVESTIGATING AND CLASSIFYING THE 3 ROCK TYPES

BOX OF ROCKS

IGNEOUSGRANITEGABBROOBSIDIANPUMICESCORIA

GARNET MICA SCHIST

PHYLLITESOAPSTONE

(SCHIST)MARBLEAMPHIBOLITE

WHAT’S IN THE BOX?

METAMORPHIC

SEDIMENTARYSANDSTONEOIL SHALELIMESTONEFOSSIL

LIMESTONEROCK GYPSUM

WHAT’S IN THE BOX (CONT)

Igneous rocks form from cooled molten material

If magma crystallizes underground, then the rock is INTRUSIVE

If lava cools above ground, then the rock is EXTRUSIVE

At one point in Earth’s history, all rock was igneous

IGNEOUS

IGNEOUSGRANITE (intrusive)

Large, interlocking crystalsForms from slow

crystallization of magmaComposition:

QuartzFeldsparMica

“Dimension Stone”Hard (resists scratching)Strong (bears much weight)Inert (resists weathering)Polishes brilliantly

IGNEOUSGABBRO (intrusive)

Course grainedUsually dark green“Black Granite”Composition

PlagioclaseAugiteVery little quartz

UsesCemetery markersCounter topsFloor tiles

IGNEOUSOBSIDIAN

(extrusive)Molten lava cools

quickly (extrusive)“Volcanic glass”Composition

No mineralsMost is at least a

few million years oldNot found east of

the MississippiUsed as a cutting

tool

IGNEOUSPUMICE (extrusive)

Lava cools during flight, forming pores

During an explosive volcanic eruption, may rain down from the sky

High silica contentUses:

Abrasives for cleanersScouring agentsInsulation

IGNEOUSSCORIA (extrusive)

Often forms as the top of a lava flow cools

Many of the same uses as pumice

Porous, lightHigher basalt

content than pumice, giving it a red to black color

These form from existing rocks that are chemically changed by high heat and/or pressure

Parent rocks can be igneous, metamorphic, or sedimentary

METAMORPHIC

METAMORPHICSCHIST

Intermediate; between phyllite and gneiss

Foliated (low-grade)Contains lots of

mica, which allows it to split into pieces

Garnet mica schist contains small garnet crystals (dark red)

METAMORPHICPHYLLITE

Well defined foliation

Made of mostly fine-grained mica

Intermediate; between slate and schistFormed from

morphed shales or mudstones

Sedimentary layers have been preserved

Orange tint indicates presence of iron

METAMORPHICTALC SCHIST

(SOAPSTONE)Extremely softSoapy or greasy textureTalc

Softest mineral on EarthUsed in baby powderSome areas of the San

Andreas Fault contain soapstone Limits severity and

frequency of earthquakesAlabaster, serpentine

METAMORPHICMARBLE

Recrystallized limestone or dolemite, hence the white color

Composed entirely of one mineral: calcite

Often found interbedded with schists, phyllites, gneisses, and granulites

If the marble has other colors, it is because of impurities in the original limestone deposit

Uses:Buildings, monuments,

tabletops

METAMORPHICAMPHIBOLITE

Parent rocks:Basalt, gabbro,

dolemite (sedimentary)

Medium to coarse-grained crystals

Hornblende and plagioclaste (ex.)

SEDIMENTARYSedimentary rocks

form from pieces and parts of older rocks, plants, skeletons, shells, or other debris

Most of the rock in our area is sedimentary, like sandstone and slate

Sedimentary rocks are the only rocks that we find fossils in

SEDIMENTARYLIMESTONE

Composed primarily of CaCO3 (calcium carbonate), or calcite

Forms underwater, from shells and skeletons of dead sea creatures

Fossil richCommon in PALimestone blocks were

used to construct the Great Pyramid of Egypt

SEDIMENTARYSANDSTONE

Clastic rock made up of fine grains of sand “glued” together by minerals (usually quartz)

Common to beaches, floodplains, deltas, and deserts

Siltstone, mudstoneA red tint indicates

the presence of clay

SEDIMENTARYOIL SHALE

Shale is extremely common in riverbeds, under, and around lakes

Forms from the compaction of silt and clay sized particles

Black shales contain organic materials that produce oil, natural gas, and coal

SEDIMENTARYROCK GYPSUM

Gypsum is a common mineral that is used in drywall, plaster, and concrete

Sulfate mineral (SO4)

Forms in cavesSatin spar gypsum

and alabaster are used in decorative pieces

ROCK ON!And thank you geology.com for all your

useful info and pictures!