Review of Minerals  What are the four characteristics of • Naturally Occurring • Crystalline Solid • Specific Chemical Composition • Inorganic a mineral? Review of Minerals  What mineral  DOLOMITE is this? Review of Minerals  What mineral  QUARTZ is this? Review of Minerals  What mineral  GALENA is this? Review of Minerals  What mineral  OLIVINE is this? Review of Minerals  What mineral is this?  ORTHOCLASE FELDSPAR Review of Minerals  What mineral  HEMATITE is this? Review of Minerals  What mineral  FLOURITE is this? Review of Minerals  What mineral  GY PSUM is this? Metamorphism is Described by Texture, Index minerals, Grade, and Facies Identifying Metamorphic Rocks  Step • Determine the rock texture  Foliated textures – rocks exhibit foliation… layering or parallel alignment of platy or flat mineral crystals (if the rock appears layered, it is foliated) due to pressure and recrystallization  Nonfoliated textures – rocks exhibit no layering, yet they may exhibit stretched fossils or long, prismatic crystals that have grown parallel to the pressure field Foliation  Determined by the degree of • Cleavage • Schistosity • Banding Increasing intensity of metamorphism Low grade Intermediate grade Increasing crystal size Increasing coarseness of foliation High grade Foliated rocks are classified by the degree of cleavage, schistosity, and banding Diagenesis Low grade Intermediate grade Slaty Rock Cleavage Phyllite Texture very flat foliation wavy or wrinkled foliation of fine grained minerals giving rock metallic luster Schistosity (abundant micaceous minerals) scaly glittery layer of visible platy minerals and/or linear alignment of long prismatic crystals High grade Gneissic Banding (fewer micaceous minerals) Migmatite alternating Banding layers or lenses of light and dark medium to coarse grained minerals Progression of metamorphism Start with a shale and then hit it with pressure and heat Slate Phyllite Schist You end up with something that is really Gneiss! Inc Pressure (kilobars) Slate rea sing met amo r Intermediate Grade Phyllite phic g de High Grade Schist Blueschist Gneiss Migmatite Temperature (°C) Depth (km) Low Grade Metamorphic Rock Textures (Unfoliated Textures) - Crystalline Texture – medium to coarse grained aggregate of intergrown, equigranular, visible crystals (example: Marble) - Microcrystalline Texture – fine grained aggregate of intergrown microscopic crystals (example: hornfels) - Sandy Texture – medium to coarse grained aggregate of fused, sand-sized grains that resemble sandstone (example: quartzite) - Glassy Texture – homogeneous texture with no visible grains or other structures and breaks along glossy surfaces (anthracite coal) Identifying Metamorphic Rocks  Step • Determine the rock’s mineralogical composition and/or other distinctive properties  Other Distinctive Features to Note  Stretched or Sheared Grains – deformed pebbles, fossils, mineral crystals, that have been stretched, shortened, or sheared  Porphyroblastic Texture – arrangement of large crystals (PORPHY ROBLASTS) set in a finer-grained groundmass (sort of sounds like porphyritic texture)  Hydrothermal Veins – fractures filled by minerals that precipitated from hydrothermal fluids With increasing metamorphic Mineral suites define grade, mineral composition metamorphic facies changes  Step Identifying Metamorphic Rocks • Use Five Step Chart for Metamorphic Rock Analysis to determine the name of the rock you are identifying  Step • Based on the name of the identified metamorphic rock, name the rock it was before metamorphism (this is the metamorphic rocks “parent” rock or protolith) Metamorphism of Sedimentary Rocks Protolith Sandstone: Quartzite, Metaquartzite Shale: Slate Phyllite Schist Gneiss Limestone: Marble Metamorphism of Igneous Rocks For most purposes, just put “meta” in front of the protolith name Examples: metabasalt metarhyolite If a mafic or intermediate metamorphic rock is dominated by amphibole and feldspars: -Amphibolite [...]... from space, from organisms, or from the breakdown of other rocks and minerals *Environmental changes and processes affect the rock forming materials and existing rocks *These changes and processes produce 3 distinct groups of rocks **IGNEOUS **SEDIMENTARY **METAMORPHIC Igneous Rocks What is an igneous rock?  Crystalline or glassy rocks formed from the cooling and solidification of molten magma (below... surface)/lava (on Earth’s surface)  Compose the majority of the earth  Can use the texture and mineralogy of these rocks to determine where in the Earth they formed Igneous Rock Textures  Where the rock forms in the Earth and how quickly it cools determines what kind of texture it will have Cooling Rates and Igneous Textures  The slower the crystals form, the larger they will be Deep =Hot =Slow Cooling=Large... this? Goals for this lab  Learn the basics of rock identification  Learn how to distinguish between 3 rock types  Observe hand samples and infer how they might have been formed *Solid aggregate of mineral grains, mineral crystals, or other rocks *Some exceptions **Obsidian is made of volcanic glass **Coal is made of plant fragments *The materials forming rocks come from the Earth’s mantle as magma,... influence rock type Minerals in Igneous Rocks Cont Chemistry changes influence rock type Mineralogy cont  Felsic rocks • dominated by K-feldspar, Na Plagioclase, quartz, and biotite • usually light in color • typical of continental crust (Granite and Rhyolite)  Intermediate rocks • dominated by plagiocase, amphibole, pyroxene, biotite, quartz • intermediate color • Andesite and diorite  Mafic rocks. .. Ca-Plagioclase, pyroxene, olivine, amphibole • Usually dark in color • Typical of oceanic crusts (and the Moon, Mars, and Venus!) (Basalt, • Gabbro)  Ultramafic rocks • Dominated by olivine, minor amounts of pyroxene and Ca-plagioclase • Rarely seen on Earth’s surface • Major constituent of Earth’s Mantle • Peridotite Sedimentary Rocks ... Cooled slowly and then abruptly brought near surface and cooled quickly =both large and small crystals =Porphyritic  Cooled extremely quickly =Glassy  Cooled quickly and bubbles present =Vesicular  Explosive welding of materials from volcanism = Pyroclastic/Fragmental  Igneous Rock Textures Glassy Vesicular Pyroclastic/Fragmental What minerals are present also determine what kind of Igneous Rock forms