METAMORPHIC ROCKS MEANS “CHANGED SHAPE” DEFINED AS A ROCK THAT HAS UNDERGONE CHEMICAL AND/OR PHYSICAL CHANGES METAMORPHIC TYPES/SCALES PROCESSES CAUSING 1) CONTACT METAMORPHISM METAMORPHISM –SMALL SCALE METAMORPHISM USUALLY CAUSED WHEN 1) HEAT MAGMA BURNS THE SURROUNDING COUNTRY ROCK 2) PRESSURE 2) REGIONAL METAMORPHISM –LARGE SCALE METAMORPHISM 3) CHEMICAL REACTIONS USUALLY CAUSED BY TECTONIC WITH HOT FLUIDS PRESSURE PHYSICAL CHANGES Figure 8.6 DURING METAMORPHISM 1) REORIENTATION OF ROD OR PLATE SHAPED MINERALS 2) RECRYSTALLIZATION OF MINERALS RESULTING IN LESS BUT LARGER GRAINS 3) CREATION OF NEW MINERALS – SOME INDEX MINERALS CAN TELL YOU WHAT PRESSURE AND HEAT CONDITIONS THE ROCK REACHED 1 Metamorphism of Sedimentary Rocks Cleavage (metamorphic) Bedding (sedimentary) Slaty cleavage (forms perpendicular to maximum stress) cutting Original bedding of sedimentary rock. METAMORPHIC ROCK TEXTURES 1) FOLIATED – ROD OR PLATE SHAPED MINERALS HAVE LINED UP SO THAT ONE DIRECTION HAS A DOMINANT FABRIC STRUCTURE 2) NONFOLIATED – MINERALS HAVE NO DIMENSION LONGER OR SHORTER THAN ANY OTHER SO NO FABRIC PATTERN APPEARS 2 FOLIATED ROCKS •SLATE –CRYSTALS TOO SMALL TO SEE HAVE LINED UP –USED FOR POOL TABLE TOPS AND CHALK BOARDS FOLIATED ROCKS •SLATE •PHYLLITE –CRYSTALS HAVE GROWN SO THAT THEY ARE ALMOST VISIBLE GIVE THE ROCK A VELVETY SHEEN FOLIATED ROCKS •SLATE • PHYLLITE •SCHIST –CRYSTALS HAVE GROWN LARGE ENOUGH TO SEE 3 FOLIATED ROCKS •SLATE • PHYLLITE •SCHIST • GNEISS –MAFIC AND FELSIC MINERALS HAVE SEPARATED TO MAKE DARK AND LIGHT BANDS FOLIATED ROCKS METAMORPHISM •SLATE INCREASING • PHYLLITE •SCHIST • GNEISS One More Foliated Rock •A rock made of pebbles of another rock can be “squished” •Metaconglomerate 4 NONFOLIATED Stylolites in marble METAMORPHIC ROCKS 1) MARBLE –EFFERVESCES WITH HCl BUT DOESN’T SCRATCH GLASS 2) QUARTZITE –CAN SCRATCH GLASS BUT DOESN’T EFFERVESCE IN HCl CONTACT METAMORPHISM • HORNFELS IS THE GENERAL TERM APPLIED TO THE WIDE VARIETY OF RATHER HARD, NONFOLIATED METAMORPHIC ROCKS FORMED DURING CONTACT METAMORPHISM 5 Metamorphic country rock (gneiss) Contact metamorphosis Igneous /baked zone intrusion (hornfels) 6 7.