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A ROCK IS A GROUP OF MINERALS BOUND TOGETHER IN SOME WAY.

ROCKS ARE DIVIDED INTO THREE GROUPS BASED ON HOW THE ROCKS FORMED

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IGNEOUS ROCKS ARE FORMED BY THE COOLING AND HARDENING OF MOLTEN ROCKS.

INTRUSIVE (PLUTONIC) - FORM BELOW THE EARTH’S SURFACE

EXTRUSIVE (VOLCANIC) – FORM ABOVE THE EARTH’S SURFACE

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TEXTURE REFERS TO THE SIZE OF THE CRYSTALS IN AN IGNEOUS ROCK

THERE ARE TWO PHYSICAL PROPERTIES OF IGNEOUS ROCKS USED IN THE IDENTIFICATION OF THE ROCK NAME.

**THE LARGER THE CRYSTAL SIZE THE DEEPER WITHIN THE EARTH THE ROCK FORMED www.oiexploration.ir

COLOR REFERS TO THE MINERAL COMPOSITION OF THE ROCK.

IT IS IDENTIFIED BY USING THE GENERAL SHADE OF THE ROCK.

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- IF THERE ARE MORE LIGHT MINERALS THAN IT IS LIGHT

- IF THERE ARE MORE DARK MINERALS THAN IT IS DARK

- IF THERE IS THE SAME AMOUNT OF DARK MINERALS AS LIGHT THAN IT IS MEDIUM

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Intrusive (plutonic) Igneous Rocks

MAGMA IS MOLTEN ROCK UNDERNEATH THE EARTH’S SURFACE.

INTRUSIVE IGNEOUS ROCKS COOL SLOWLY DEEP WITHIN THE EARTH AND PRODUCES LARGE CRYSTALS

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INTRUSIVE IGNEOUS ROCKS WILL RESULT IN A VERY COARSE (PEGMATITE) OR COARSE (PHANERITIC) TEXTURE (EX. GRANITE)

PEGMATITE GRANITEwww.oiexploration.ir

Extrusive (volcanic) igneous rocks

LAVA IS MOLTEN ROCK THAT POURS OUT ONTO THE EARTH’S SURFACE.

EXTRUSIVE ROCKS LACK DISTINCT MINERAL GRAINS DUE TO RAPID COOLING OF LAVA AT OR NEAR THE EARTH’S SURFACE

EXTRUSIVE IGNEOUS ROCKS WILL RESULT IN FINE (APHANITIC) TEXTURE (EX. BASALT)

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IF THE COOLING IS INSTANTANEOUS A GLASSY TEXTURE MAY FORM (EX. OBSIDIAN)

IF GAS BUBBLES ARE TRAPPED AS THE LAVA RAPIDLY COOLS A VESICULAR TEXTURE MAY OCCUR (PUMICE)

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PORPHYRITIC ROCKS

- CONTAINS TWO STAGES OF COOLING

- COOLS FIRST AT GREAT DEPTH FORMING LARGE CRYSTALS STILL SURROUNDED BY MAGMA

- IT IS THEN RUSHED TO THE SURFACE AND THE REMAINING LIQUID AROUND IT COOLS QUICKLY FORMING FINE-GRAINED CRYSTALS

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GRANITE- QUARTZ, ORTHOCLASE FELDSPAR, AND AT LEAST ONE OTHER MINERAL; LIGHT-COLORED; COARSE-GRAINED; MAKES UP CONTINENTS; FELSIC

RYOLITE- FINE-GRAINED GRANITE; FELSIC

OBSIDIAN- VOLCANIC GLASS; RAPID COOLING; PYROCLASTIC; FELSIC

PUMICE- SPONGE-LIKE BECAUSE OF ESCAPING AIR BUBBLES DURING COOLING; FELSIC www.oiexploration.ir

BASALT- FINE-GRAINED; DARK-COLORED; MAKES UP THE OCEAN FLOOR; MAFIC

GABBRO- COARSE-GRAINED BASALT; MAFIC

DIABASE- GRAIN SIZE INBETWEEN BASALT AND GABBRO; MAFIC

BASALT GLASS- MAFIC OBSIDIAN

SCORIA- MAFIC PUMICE

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