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Metamorphic Rocks “changed rocks” – can form from: sedimentary, igneous or other metamorphic rocks * Not that kind of change..... Agents of Metamorphism: A. Heat: but not hot enough to melt rock (melted rocks reform into igneous rocks) B. Pressure: from burial at great depths or stress from mountain building (squeezing) activity Agents of Metamorphism cont... C. Chemically active fluids: mainly water that can carry new ions that can bond to original rock This picture shows potentials spots for all 3 agents of metamorphism. Where are they? Degrees of Metamorphism: * shows in rock’s texture or mineral make-up Low grade: subjected to relatively mild heat or pressure often hard to distinguish from original rock i.e. shale (igneous) → slate (meta.) The top 2 are shale. The bottom 2 are slate. Which one is harder? High-grade: subjected to high heat or pressure - original rock features hard to see i.e. quartz sandstone (sed rock often w/ fossils) → quartzite Metamorphic settings (areas) Regional: over large areas (generally mtn building) * Produces greatest amt of metamorphic rock Contact: occurs near a mass of magma & bakes surrounding rock What areas in this picture would be affected by contact metamorphism? Which by regional? Metamorphic Textures Foliated: minerals are parallel lined up, like pages in a book slates: fine-grained, easily split schists: strongly foliated, “platy” gneiss: silicate minerals obviously segregated, banded A B So which is the slate, schist and gneiss? C Non-Foliated: contain equal sized crystals, looks like coarse igneous rock Marble: parent rock= limestone, calcite crystals Quartzite: parent rock= quartz sandstone, quartz is fused A These are microscopic thin sections of a foliated rock and a nonfoliated rock. Which is which? B Marble Which one of these samples would react with acid? Quartzite So is this sample foliated or nonfoliated?