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Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife page 1 / 10 Unit 3 Chapter 5 How Earth’s Rocks were Formed HOMEWORK: HW 1 HW 2 Topic Questions: PG. 68, 74, 79 Review, Interpret & Apply, Crit. Thinking pg 82-83 Unit 1 Igneous Rocks Topic 1 Uniformity of Process Uniformitarianism states, “the present is the key to the past” 1. the geologic processes now at work were also active in the past 2. the present physical features of Earth were formed by these same processes, at work over long periods of time. Topic 2 Three Groups of Rocks ROCKS ARE SINGLE MINERALS OR MIXTURES OF SEVERAL MINERALS THAT MAKE UP AN ESSENTIAL PART OF THE EARTH'S CRUST. THE MOST COMMON ROCKS ON EARTH ARE THOSE FORMED FROM THE COOLING AND SOLIDIFICATION OF LIQUID ROCK, CALLED MAGMA, AND ARE CALLED IGNEOUS ROCKS. SEDIMENTARY ROCKS FORM FROM WEATHERED SEDIMENT OF IGNEOUS, METAMORPHIC, OR OTHER SEDIMENTARY ROCKS THAT ARE CARRIED FROM ONE PLACE TO ANOTHER, REDEPOSITED, BURIED, AND THEN HARDENED INTO ROCK. METAMORPHIC ROCKS FORM FROM PREEXISTING IGNEOUS, SEDIMENTARY, OR METAMORPHIC ROCKS AS A RESULT OF TEMPERATURE AND PRESSURE CHANGES. Topic 3 Recognizing Igneous Rocks IGNEOUS ROCKS COMPOSE 95 PERCENT BY VOLUME OF THE CRUST OF THE EARTH. THEY ARE THE PARENT MATERIALS FOR ALL OTHER KINDS OF ROCK. IGNEOUS ROCKS ARE THOSE THAT HAVE BEEN FORMED BY THE SOLIDIFICATION OF MOLTEN ROCK MATERIAL (MAGMA). IF LIQUID ROCK FLOWS OUT ON TO THE SURFACE OF THE EARTH IT IS CALLED LAVA. PLUTONIC (INTRUSIVE) ROCKS FORM BELOW THE SURFACE. THEY HAVE DISTINCT CRYSTALS OR COURSE TEXTURE. Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife page 2 / 10 VOLCANIC (EXTRUSIVE) ROCKS FORM ON THE EARTH'S SURFACE. THEY HAVE VERY SMALL OR MICROSCOPIC CRYSTALS OR FINE TEXTURE Topic 4 KINDS OF MAGMA FELSIC (GRANITIC) MAGMA - THICK, STIFF MAGMA THAT FORMS JUST BELOW THE CRUST. LIGHT COLORED VISIBLE CRYSTALS DUE TO HIGH FELDSPAR AND SILICA CONTENT. MAFIC (BASALTIC) MAGMA - MAGMA THAT ORIGINATES IN THE MANTLE AND FLOWS READILY FORMING THIN LAYERS, ESPECIALLY ON THE OCEAN FLOOR. DARK FINE TEXTURED ROCKS DUE TO MAGNESIUM AND IRON (OLIVINE) CONTENT. Topic 5 Textures of an Igneous Rock THE TERM TEXTURE IN IGNEOUS ROCK REFERS TO THE SIZE, SHAPE, AND ARRANGEMENT OF THE COMPONENT MINERAL GRAINS. (CRYSTALS) CRYSTAL SIZE DEPENDS ON HOW FAST THE MAGMA (LAVA) COOLS. THE LONGER IT COOLS, THE LARGER THE CRYSTALS. INTRUSIVE IGNEOUS ROCKS - ARE GENERALLY COARSE-GRAINED BECAUSE THE SLOW RATE OF COOLING ALLOWS TIME FOR LARGE CRYSTAL GROWTH. EXAMPLE: GRANITE EXTRUSIVE IGNEOUS ROCKS - GENERALLY HAVE VERY SMALL TO NO CRYSTALS BECAUSE OF RAPID COOLING. EXAMPLE: BASALT, OBSIDIAN Topic 6 PORPHYRITIC TEXTURE PORPHYRIES - ARE ROCKS WITH TWO OR MORE CRYSTAL SIZES DUE TO DIFFERENT COOLING RATES. A ROCK HAVING LARGER EARLIER FORMED CRYSTALS THAT ARE SURROUNDED BY LATER FORMED SMALLER CRYSTALS. Topic 7 FAMILIES OF IGNEOUS ROCKS Topic 8 DESCRIPTION OF COMMON IGNEOUS ROCKS Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife page 3 / 10 GRANITE FAMILY FORMS FROM FELSIC MAGMAS. LIGHT COLORED ORTHOCLASE AND QUARTZ ARE DOMINANT. GRANITE IS MADE OF QUARTZ, ORTHOCLASE FELDSPAR, AND MICA. GRANITE HAS COURSE-GRAIN TEXTURE. (INTRUSIVE) OBSIDIAN IS VOLCANIC GLASS WITH MICROSCOPIC TEXTURE. ROCK FORMED WHEN LAVA COOLS IN WATER. VERY HARD. CONCHOIDAL FRACTURE. PUMICE IS FORMED FROM FELSIC LAVA THAT HARDENED WHILE STEAM AND GASES WERE STILL BUBBLING OUT OF IT. (SOMETIMES FLOATS) GABBRO FAMILY FORMS FROM MAFIC MAGMAS. DARK COLORED GABBRO IS DARK COLORED, COURSE-GRAIN TEXTURE. (INTRUSIVE) BASALT GLASS IS A DARK COLORED EQUIVALENT OF OBSIDIAN. SCORIA IS A DENSER, DARK COLORED EQUIVALENT OF PUMICE (NEVER FLOATS) DIORITE FAMILY HAS A COMPOSITION AND COLOR BETWEEN THE GRANITE AND GABBRO FAMILIES. DIORITE IS COURSE GRAINED. ANDESITE IS FINE GRAINED. Unit 2 SEDIMENTARY ROCKS SEDIMENTARY ROCKS COVER 75 PERCENT OF THE SURFACE OF THE EARTH, YET MAKE UP ONLY 8 PERCENT OF THE VOLUME OF THE EARTH'S CRUST. (UPPER 2 MI, IGNEOUS 15 MI) TOPIC 10 HOW CLASTIC ROCKS FORM WEATHERING - THE PROCESSES BY WHICH ROCKS ARE PHYSICALLY BROKEN INTO SMALLER PARTICLES AND CHEMICALLY DECOMPOSED. (CHANGE) TWO PROCESSES: DISINTEGRATION - THE PHYSICAL DISINTEGRATION OR BREAKING OF SOLID MASSES OF ROCK INTO LOOSE SMALLER FRAGMENTS. THERE IS NO CHEMICAL CHANGE IN THE ROCK. Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife page 4 / 10 ROCKS ARE BROKEN INTO FRAGMENTS BY: 1. PLANTS AND THEIR ROOTS. 2. PERIODIC FREEZING OF WATER (ICE WEDGING). WATER EXPANDS BY ABOUT 9 % WHEN IT FREEZES AND IS CAPABLE OF EXERTING THOUSANDS OF POUNDS OF PRESSURE PER SQUARE INCH. 3. SHEETING - IS A PROCESS IN IGNEOUS ROCKS (GRANITE) WHERE THE ROCK EXPANDS FORMING CRACKS PARALLEL TO THE SURFACE AFTER ROCK MATERIAL HAS BEEN REMOVED FROM ABOVE. DECOMPOSITION - THE CHEMICAL SEPARATION OF MINERALS AND ROCKS INTO ELEMENTS OR SIMPLER COMPOUNDS. RAINWATER CONTAINS CARBON DIOXIDE WHICH FORMS CARBONIC ACID. SULFUR AND NITROGEN IN THE AIR FORMS SULFURIC AND NITRIC ACIDS (ACID RAIN) DECAYING ORGANIC MATTER FORMS HUMIC ACID IN THE SOIL. TOPIC 11 SORTING OF SEDIMENTS EROSION - IS THE PROCESS BY WHICH WEATHERING PRODUCTS ARE CARRIED AWAY (TRANSPORTED) AND REDEPOSITED BY WIND, WATER, GRAVITY, OR ICE. AS WIND AND WATER SLOW DOWN, THEY LOOSE (KINETIC) ENERGY TO CARRY MATERIAL. THEY WILL DROP THE HEAVIEST PARTICLES (ROCKS) FIRST AND NEXT HEAVIEST PARTICLES SECOND (SAND) AND THE LIGHTEST PARTICLES LAST (SILT AND CLAY). THIS RESULTS IN SORTING OF ERODED SEDIMENT BY SIZE OR MASS. TOPIC 9 KINDS OF SEDIMENT SEDIMENT - SMALL PARTICLES BROKEN DOWN FORM SOLID ROCK. SEDIMENTS MAY CONSIST OF FRAGMENTS OF IGNEOUS, METAMORPHIC, OR OLDER SEDIMENTARY ROCKS. SEDIMENTARY ROCKS ARE IDENTIFIED AND NAMED ACCORDING TO THEIR COMPOSITION AND TEXTURE. Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife page 5 / 10 TWO GENERAL TYPES OF SEDIMENTARY ROCK: CLASTICS - ARE ROCKS COMPOSED OF PARTICLES OF CLAY, SILT, SAND, AND GRAVEL, OR FRAGMENTS OF PARENT ROCK OR FOSSILS. CLASTIC ROCKS ARE NAMED ACCORDING TO THE SIZE AND SHAPE OF THE FRAGMENTS (TOPIC 12 CONGLOMERATE, SANDSTONE, & SHALE 1. CONGLOMERATES - ARE MIXTURES OF ROUNDED PEBBLES OF ANY KIND OR SHAPE. 2. BRECCIA - SIMILAR TO CONGLOMERATES EXCEPT FRAGMENTS ARE SHARP ANGULAR PIECES. 3. SANDSTONES - USUALLY CONSIST OF SMALL QUARTZ GRAINS, BUT MAY BE COMPOSED OF CALCITE, FELDSPAR OR OTHER MINERAL FRAGMENTS. (.2 TO 2 mm) 4. SILTSTONE - IS LIKE STANDSTONE BUT WITH SMALLER GRAINS THAT CAN BE FELT BUT ONLY SEEN WITH MAGNIFICATION. (.005 TO .1 mm) 5. SHALE - IS MADE OF THIN LAYERS OF CLAY AND MUD TOO SMALL TO BE SEEN WITHOUT MAGNIFICATION. ( < .004 mm) FORMED BY COMPACTION ALONE. ALL CLASTIC ROCKS UNDERGO SOME KIND OF CONSOLIDATION PROCESS (LITHIFICATION) THE PROCESS OF CONVERTING SEDIMENT INTO SEDIMENTARY ROCK IS CALLED LITHIFICATION AND INVOLVES CEMENTATION AND COMPACTION. CEMENTATION - THE PROCESS WHICH INVOLVES THE PRECIPITATION OF MINERALS IN THE PORE SPACES BETWEEN PARTICLES OF THE SEDIMENT. THE PRECIPITATION, CALLED CEMENT, IS MOST OFTEN EITHER CALCITE (CaCO3) OR SILICA (SiO2). COMPACTION - A PROCESS BY WHICH SEDIMENTS IMPERMEABLE - FLUIDS ARE NOT ABLE TO MOVE THROUGH IT. (SHALE) PERMEABLE (POROUS) - LIQUID CAN MOVE THROUGH. OIL OR WATER MAY ACCUMULATE IN PORE SPACES IN THESE ROCKS. (SANDSTONE) NONCLASTIC ROCKS FORM BY CHEMICAL OR BIOCHEMICAL (ORGANIC) PRECIPITATION. (FROM SOLUTION) (TOPIC 9) Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife page 6 / 10 TOPIC 13 SEDIMENTARY ROCKS OF CHEMICAL ORIGIN PRECIPITATES - OCCUR WHEN CHEMICAL REACTIONS FORM A SOLID THAT SETTLES OUT OF SOLUTION. (CALCITE CRYSTALS IN CAVES) 1. LIMESTONE - COMPOSED OF CALCITE; MOST ASSOCIATED WITH SEAS AND BIOLOGICAL PROCESSES OF CORALS AND OTHER MARINE ORGANISMS. 2. CHALK - IS A VARIETY OF LIMESTONE CONSISTING OF CALCITE AND SHELLS (MICROSCOPICALLY SMALL) 3. FLINT OR CHERT - COMPOSED OF SILICA; AND THOUGHT TO HAVE FORMED FROM ACCUMULATIONS OF SILICEOUS REMAINS OF DIATOMS AND RADIOLARIA. EVAPORATES - FORM WHEN WATER EVAPORATES, LEAVING ITS DISSOLVED SOLIDS BEHIND. (BEDS OF SALT AND GYPSUM) 4. ROCK SALT - COMPOSED OF HALITE; FORMED AS A RESULT OF THE EVAPORATION OF SALINE WATER BODIES. 5. ALABASTER - GYPSUM; FORMED BY EVAPORATION. TOPIC 14 SEDIMENTARY ROCKS OF ORGANIC ORIGIN 6. COAL - RESULTS FROM THE ACCUMULATION OF PLANT MATTER IN SWAMPY ENVIRONMENTS AND THEN BIOCHEMICALLY AND PHYSICALLY CONSOLIDATED INTO A CARBON RICH MATERIAL. BITUMINOUS - SOFT COAL ANTHRACITE - HARD COAL ORGANIC DEPOSITS RESULT FROM LIFE PROCESSES. TOPIC 15 SEDIMENTARY FEATURES THE ENVIRONMENT OF DEPOSITION IS THE LOCATION WHERE SEDIMENT IS BEING DEPOSITED. THE THREE MAJOR ENVIRONMENTS OF DEPOSITION ARE THE MARINE, CONTINENTAL, AND TRANSITIONAL ENVIRONMENTS. COMPARING PRESENT-DAY SEDIMENTARY DEPOSITS TO OLD SEDIMENTARY ROCKS PERMITS ONE TO RECONSTRUCT CONDITIONS OF THE EARTH AS THEY WERE HUNDREDS OF MILLIONS OF YEARS AGO. Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife page 7 / 10 UNIFORMITARIANISM - (HUTTON) GEOLOGICAL PRINCIPLE THAT STATES THAT GEOLOGICAL PROCESSES OF THE PRESENT ARE SIMILAR TO PROCESSES OF THE PAST. (EROSION) SEDIMENTS AND THUS SEDIMENTARY ROCK ARE DEPOSITED IN LAYERS. THE OLDEST BED (LAYER) IS DEPOSITED FIRST AT THE BOTTOM OF THE SERIES OF LAYERS. (LAW OF SUPERPOSITION) SEDIMENT WILL BE DEPOSITED WHENEVER THERE IS INSUFFICIENT ENERGY TO CARRY IT FURTHER. CROSS-BEDDING IS AN ARRANGEMENT OF BEDS IN WHICH ONE SET OF LAYERS IS INCLINED RELATIVE TO THE OTHERS. OFTEN INDICATIVE OF PASS CHANGES IN WIND OR WATER CURRENTS. TOPIC 16 FOSSILS IN SEDIMENTARY ROCKS FOSSIL - IS ANY RECORD (FOSSILIZED OR IMPRESSIONS) OF PAST LIFE SUCH AS A BONE, SHELL, OR OTHER HARD PART OF AN ANIMAL OR PLANT. TOPIC 17 RIPPLE MARKS AND MUD CRACKS RIPPLE MARKS - ARE COMMON FEATURES THAT FORM ON DUNES OR ON BEACHES AND ARE USEFUL IN INDICATING WIND OR WATER CURRENTS AND THE TOPS OF STRATA. FORMED BY THE PROCESS OF CEMENTATION. MUD CRACKS - FORM ALONG SHORES OR IN RIVER BEDS. THEY DEVELOP WHEN FINE-GRAINED SEDIMENTS SHRINK ON DRYING, SAND IS BLOWN IN TO CRACKS, THEN CONSOLIDATED. TOPIC 18 NODULES, CONCRETIONS, GEODES CONCRETIONS - ARE BALL-LIKE OBJECTS OR IRREGULARLY SHAPED MASSES OF CEMENTING MATERIAL COLLECTED AROUND A NUCLEUS OF BONE OR OTHER FOSSILIZED MATERIAL, A MUDBALL, OR A MASS OF SANDSTONE. GEODES - ARE HOLLOW, BALL-LIKE OBJECTS SOMETIMES FOUND IN LIMESTONE. QUARTZ AND OTHER MINERAL CRYSTALS GROW INWARD FROM A HARD OUTER RIM OF SILICA. Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife page 8 / 10 Unit 3 METAMORPHIC ROCKS TOPIC 10 WHAT METAMORPHIC ROCKS ARE METAMORPHIC ROCKS - FORM FROM PRE-EXISTING IGNEOUS, SEDIMENTARY, OR METAMORPHIC ROCKS AS A RESULT OF TEMPERATURE AND PRESSURE AND ASSOCIATED CHEMICAL SOLUTIONS. METAMORPHIC ROCKS ARE THE LEAST ABUNDANT OF THE THREE ROCK CLASSES. THREE CHANGES OCCUR AS THE RESULT OF METAMORPHISM: 1 A REARRANGEMENT OF MINERAL GRAINS FOLIATION - IS THE ARRANGING OF ROCKS INTO LAYERS TO OCCUPY THE LEAST POSSIBLE SPACE. FOLIATION IS PRIMARILY THE RESULT OF DYNAMIC (PRESSURE) METAMORPHISM. 2 RECRYSTALLIZATION - OR ENLARGEMENT OF CRYSTALS 3 A CHANGE IN THE CHEMISTRY OF THE ROCK THAT RESULTS IN RECOMBINATION OF ELEMENTS TO FORM DIFFERENT MINERALS. METASOMATISM - IS THE GROWTH OF NEW MINERALS (CHEMICAL CHANGES) DUE TO AN EXCHANGE OF IONS BETWEEN THE ORIGINAL ROCK AND HIGH TEMPERATURE FLUIDS MOVING THROUGH THE ROCK. TYPES OF METAMORPHISM TOPIC 20 REGIONAL METAMORPHISM REGIONAL METAMORPHISM - METAMORPHISM OVER EXTENSIVE AREAS AS A RESULT OF INTENSE COMPRESSION ASSOCIATED WITH THE CONVERGENCE OF TECTONIC PLATES DURING MOUNTAIN BUILDING. (12 - 15 km) METAMORPHISM ASSOCIATED WITH MOUNTAIN BUILDING DECREASES IN RANK (SEVERITY) OUTWARD FROM THE MOUNTAIN CORE. BURIAL METAMORPHISM - CHANGES OCCUR DUE TO THE WEIGHT OF OVERLYING ROCK WHICH CAUSES REORIENTATION OF MINERAL GRAINS WITHIN THE ROCK. (12 - 15 km) TOPIC 22 CONTACT METAMORPHISM CONTACT METAMORPHISM - OCCURS AT OR NEAR THE CONTACTS BETWEEN HOT IGNEOUS MATERIAL AND COUNTRY ROCK. HEAT IS THE MOST IMPORTANT AGENT IN CONTACT METAMORPHISM. W/IN 2 km. IN VARYING AMOUNTS, LIQUIDS AND GASES ARE ALWAYS PRESENT AND REACT WITH ELEMENTS IN THE COUNTRY ROCK. Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife page 9 / 10 UNUSUAL MINERALS ARE FOUND AT THE CONTACT ZONE. TWO GENERAL GROUPS OF METAMORPHIC ROCKS: FOLIATED ROCKS - INCLUDE ROCKS WITH MINERALS ALIGNED IN BANDS. SLATE - IS A PRODUCT OF REGIONAL METAMORPHISM OF CLAYEY ROCKS, PARTICULARLY SHALE. REPRESENT THE LOWEST RANK OF METAMORPHIC ROCKS, THUS LITTLE LAYERING (TOPIC 21 THE METAMORPHISM OF SHALE) SCHISTS - ROCKS IN WHICH RECRYSTALLIZATION HAS OCCURRED FORMING LAYERS (FOLIATION) OF BIOTITE, FELDSPAR AND QUARTZ. SCHISTS ARE THE MOST ABUNDANT METAMORPHIC ROCKS AND ARE ASSOCIATED WITH MEDIUM-GRADE METAMORPHISM. GNEISS - IS A COARSE-GRAINED COARSELY BANDED METAMORPHIC ROCK THAT LOOKS LIKE GRANITE. IT HAS ROUGH LAYERING OF BIOTITE AND REPRESENTS THE MAXIMUM RANK OF METAMORPHISM. (MINERALS HAVE SEGREGATED) NONFOLIATED ROCKS - SHOW LITTLE, IF ANY, ORIENTATION OF GRAINS. THEY HAVE UNDERGONE INTERNAL CHANGES (RECRYSTALLIZATION). MARBLE - IS A FINE TO COARSELY CRYSTALLINE ROCK COMPOSED OF CALCITE. LIMESTONE IS THE PARENT ROCK FOR MARBLE. ENLARGEMENT OF CRYSTALS TAKES PLACE DURING METAMORPHISM. QUARTZITE - IS A FINE-GRAINED ROCK COMPOSED OF INTERGROWN QUARTZ GRAINS AND SILICA CEMENT. QUARTZITES ARE DERIVED FROM QUARTZ SANDSTONE. BITUMINOUS COAL METAMORPHIZES INTO ANTHRACITE COAL WHICH IN TURN METAMORPHIZES INTO GRAPHITE AND FINALLY DIAMONDS. TOPIC 23 THE ROCK CYCLE THE ROCK CYCLE EARTH MATERIALS CONSTANTLY CHANGE. SOME CHANGES OCCUR BELOW THE SURFACE, OTHERS OCCUR AT THE SURFACE. SOME CHANGES ARE THE RESULT OF CHEMICAL PROCESSES, SOME ARE DUE TO PHYSICAL PROCESSES. BENEATH THE SURFACE, THE FORCES OF HEAT AND PRESSURE CHANGE ROCKS. ONE SOURCE OF THIS HEAT AND PRESSURE IS THE MASS OF OVERLYING ROCKS. Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife page 10 / 10 ANOTHER HEAT SOURCE RESULTS FROM THE DECAY OF RADIOACTIVE ELEMENTS IN ROCKS. THE FOLLOWING FIGURE SHOWS THE CHANGES THAT ROCKS MAY UNDERGO. THESE CHANGES ARE REFERRED TO AS THE ROCK CYCLE. MATTER FROM THE EARTH'S CRUST IS CHANGED FROM ONE FORM TO ANOTHER. ROCK CYCLE DIAGRAM Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife Extra Notes not included in your text. (not on exam) METAMORPHIC PROCESSES: HIGH HEAT AND PRESSURE CAUSE METAMORPHISM HEAT MAY COME FROM THREE SOURCES: DECAY FROM RADIOACTIVE ELEMENTS IN THE MANTLE. AS THE NUCLEUS OF ATOMS CHANGE INTO OTHER ATOMS. NUCLEAR ENERGY IS RELEASED AS HEAT. MOST IMPORTANT SOURCE. FRICTION WHICH OCCURS DURING MOUNTAIN BUILDING (MAGMA RISING PUSHING COUNTRY ROCK ASIDE) HEAT FROM CONTACT WHEN MAGMA INTRUDES OVERLYING ROCK. THE ROCK IS ALTERED BY HEAT, SOLUTIONS, AND GASSES FROM THE MAGMA. THERMAL METAMORPHISM - INCLUDES CHANGES DUE TO HEAT. IS TYPICAL OF THERMAL METAMORPHISM. DYNAMIC METAMORPHISM - INCLUDES CHANGES CAUSED PRIMARILY BY PRESSURE (LITHOSTATIC PRESSURE) FROM BURIAL OR REGIONAL METAMORPHISM. TEXTURE - IN METAMORPHIC ROCK REFERS TO THE SIZE, SHAPE, AND ARRANGEMENT OF GRAINS. FOLIATED TEXTURE - ARE BANDS OR LAYERS CAUSED BY PARALLEL ARRANGEMENT OF MINERALS (MICA GNEISS) RECRYSTALLIZED TEXTURE - CONSISTS OF LARGE INTERLOCKING CRYSTALS 12.5 METAMORPHIC ROCK COMPOSITION QUARTZ, FELDSPAR, AND MICA ARE ALL MINERALS THAT COMPOSE IGNEOUS ROCKS. THESE SAME MINERALS ARE AMONG THE MOST ABUNDANT IN METAMORPHIC ROCKS. page 11 / 10 Earth Science Unit 3 Chap. 5 Lecture Notes B. Rife THESE MINERALS ARE THE SAME BECAUSE THEY ARE FORMED UNDER SIMILAR CONDITIONS OF PRESSURE AND TEMPERATURE. ANDALUSITE, SILLIMANITE, AND KYNITE ARE MINERALS THAT ONLY OCCUR IN METAMORPHIC ROCKS. MINERALS FORMED DURING METAMORPHISM DEPEND ON THE COMPOSITION OF THE ORIGINAL ROCK AND THE TEMPERATURES AND PRESSURES TO WHICH THE ROCK IS SUBJECTED. THE MOST STABLE MINERALS ARE FORMED UNDER LOW TEMPERATURE AND PRESSURE IN THE SEDIMENTARY LAYERS NEAR THE SURFACE. 12.6 CLASSIFICATION OF METAMORPHIC ROCKS page 12 / 10