METAMORPHIC ROCKS BEGIN
WHAT IS A METAMORPHIC ROCK? A metamorphic rock is a rock that has been changed by heat and/or pressure without completely melting.
Metamorphism metamorphism usually occurs deep underground where rocks are put under intense pressure or stress causing the rock deform metamorphism PRESSURE
Contact Metamorphism Contact Metamorphism occurs near magma or lava Contact metamorphism magma
A parent rock is the original rock that changed in a metamorphic rock metamorphic rock parent rock
There are two types of Metamorphic Rocks Foliated Nonfoliated Minerals line up due metamorphism Minerals don t line up
mineral growth without pressure Nonfoliated pressure mineral growth with pressure Foliated
Nonfoliated Foliated
P. 7 of ESRT Scheme for Metamorphic Rock Identification GRAIN TYPE OF TEXTURE SIZE COMPOSITION METAMORPHISM COMMENTS ROCK NAME MAP SYMBOL Foliated FOLIATED MINERAL ALIGNMENT BAND- ING medium Medium coarse MICA QUARTZ FELDSPAR AMPHIBOLE GARNET PYROXENE (Heat and pressure increases) Low-grade metamorphism of shale Foliation surfaces shiny from microscopic mica crystals Platy mica crystals visible from metamorphism of clay or feldspars High-grade metamorphism; mineral types segregated in bands Slate Phyllite Schist Gneiss Carbon bituminous coal Anthracite coal Nonfoliated NONFOLIATED coarse Various minerals Quartz Calcite and/or dolomite Contact (heat) or contact Various rocks changed by heat from nearby magma/lava quartz sandsne limesne or dolosne Hornfels Quartzite Marble Coarse Various minerals Pebbles may be disrted or stretched Metaconglomerate
Foliation Mineral Alignment minerals line up due pressure Banding under greater pressure minerals separate in dark and light stripes called bands
Mineral Alignment P. 7 of ESRT TEXTURE Scheme for Metamorphic Rock Identification GRAIN TYPE OF SIZE COMPOSITION METAMORPHISM COMMENTS ROCK NAME MAP SYMBOL FOLIATED MINERAL ALIGNMENT BAND- ING medium Medium coarse MICA QUARTZ FELDSPAR AMPHIBOLE GARNET PYROXENE (Heat and pressure increases) Low-grade metamorphism of shale Foliation surfaces shiny from microscopic mica crystals Platy mica crystals visible from metamorphism of clay or feldspars High-grade metamorphism; mineral types segregated in bands Slate Phyllite Schist Gneiss Banding
Intensity of Metamorphism Low-Grade Metamorphism Little change rock High-Grade Metamorphism extreme change rock
shale LOW-GRADE Sh slate ale s low ly c phyllite han ge s schist int og nei s s gneiss HIGH-GRADE
Sedimentary Rock Siltsne Shale ENTARY ROCKS............. P. 7 of ESRT TEXTURE Scheme for Metamorphic Rock Identification GRAIN TYPE OF SIZE COMPOSITION METAMORPHISM COMMENTS ROCK NAME MAP SYMBOL FOLIATED MINERAL ALIGNMENT BAND- ING medium Medium coarse MICA QUARTZ FELDSPAR AMPHIBOLE GARNET PYROXENE (Heat and pressure increases) Low-grade metamorphism of shale Foliation surfaces shiny from microscopic mica crystals Platy mica crystals visible from metamorphism of clay or feldspars High-grade metamorphism; mineral types segregated in bands Slate Phyllite Schist Gneiss As heat and pressure increases: NONFOLIATED Shale becomes Slate becomes Phyllite becomes Schist becomes Gneiss coarse Carbon Various minerals Quartz Calcite and/or dolomite Contact (heat) or bituminous coal Various rocks changed by heat from nearby magma/lava quartz sandsne limesne or dolosne Anthracite coal Hornfels Quartzite Marble
Surface of Earth 0 5 Clay deposits Inferred Shale Shale Sedimentary zone 10 Slate Depth (km) 15 20 25 Metamorphic zone Phyllite Schist Gneiss 30 0 200 400 600 800 1000 Temperature ( o C) Key At these temperatures rock melts Boundary between sedimentary zone and metamorphic zone
P. 7 of ESRT TEXTURE Scheme for Metamorphic Rock Identification GRAIN TYPE OF SIZE COMPOSITION METAMORPHISM COMMENTS ROCK NAME FOLIATED MINERAL ALIGNMENT BAND- ING medium Medium coarse MICA QUARTZ FELDSPAR AMPHIBOLE GARNET PYROXENE (Heat and pressure increases) Low-grade metamorphism of shale Foliation surfaces shiny from microscopic mica crystals Platy mica crystals visible from metamorphism of clay or feldspars High-grade metamorphism; mineral types segregated in bands Slate Phyllite Schist Gneiss The minerals in Foliated Metamorphic rocks can be determined by looking at the bar graph in the composition section
Nonfoliated rocks sometimes indicate the parent rock Carbon bituminous coal Anthracite coal NONFOLIATED coarse Various minerals Quartz Calcite and/or dolomite Contact (heat) or contact Various rocks changed by heat from nearby magma/lava quartz sandsne limesne or dolosne Hornfels Quartzite Marble P. 7 of ESRT Coarse Various minerals Pebbles may be disrted or stretched Metaconglomerate