Lab 5_Metamorphic Rock

Use the Kyanite-Andalusite-Sillimanite phase diagram to answer the following questions: Which of the three polymorphic minerals is stable at 400 o C and 0.1 giga pascals (GPa) of pressure? Andalusite Would this mineral remain stable if the temperature remained constant, but the pressure increased to 0.5 GPa? No And if not which mineral would form? Kyanite Which of the minerals is stable at 0.4 GPa and 450 o C? Kyanite If this mineral remained at 0.4 GPa of pressure, but was heated to 700 o C, which mineral would eventually form? Sillimanite Metamorphic Rocks: The third and final group of rocks to be discussed is metamorphic rocks. Metamorphic rocks are rocks that have been transformed by intense heat and pressure to form into a new rock. The texture and composition of the rock change as re-crystallization of metamorphic minerals occurs. The original rock that undergoes this transformation is known as the parent rock . The parent rock can be igneous, sedimentary, or metamorphic. Metamorphism can occur as contact metamorphism , which occurs when a pluton of magma alters the surrounding rocks by increasing the temperature and the addition of hot fluids circulating the surrounding area. Regional metamorphism occurs when a large area undergoes metamorphism due to increasing temperature or pressure. There are different metamorphic facies that you should be aware of. Facies are assemblages of different minerals that occur at different temperatures and depths. For example Hornfels facies metamorphic minerals are formed in low pressure/high temperature environments. The diagram and questions below are related to metamorphic facies. Higher temperature and pressure lead to a higher grade of metamorphism. Recall that diagenesis (shown on Figure 8.3) is the conditions under which sediment is converted to sedimentary rock. Note that diagenesis occurs at lower temperature and pressure conditions than metamorphism.

Use the flow chart below to identify the 12 rock samples you are given and fill in the chart. Metamorphic Rock Identification Foliation and Texture Description (Mineralogy) Rock Name Parent Rock Foliated Slaty cleavage - very flat foliation, compact, very fine grained Dull luster, thin flat sheets compacted together (clays, quartz and micas) Slate Increasing Metamorphic Grade Mudstone or Shale Phyllite foliation- wrinkly, crinkly, shiny, fine grained Shiny, thin wrinkly sheets (Muscovite, chlorite, quartz) Phyllite Mudstone, Shale or Slate Shcistosity- wavy foliation, very shiny, glittery, scaly Very shiny or glittery, wavy sheets (Muscovite, chlorite, quartz, can have porphyroblasts of garnet) Schist Mudstone, Shale, Slate or Phyllite Gneissic banding - alternating compositional banding, coarser grained Alternating light and dark layers; (quartz, feldspars, micas) Gneiss Mudstone, Shale, Slate, Phyllite, Schist, Granite or Diorite Foliated or Nonfoliated Medium to coarse grained Glossy, (Hornblende and plagioclase) Amphibolite Basalt, Gabbro or Ultramafic Igneous Rocks Nonfoliated Glassy, shiny texture Glassy black, uneven or conchoidal fractures Anthracite Coal Peat, Lignite, Bituminous Coal Fine grained, microcrystalline Dull luster, hard, often dark colored Hornfels Any type Microcrystalline Green-various shades, (serpentine) Serpentinite Basalt, Gabbro or Ultramafic Igneous Rocks Microcrystalline Very soft, smooth/soapy feel, can be scratched w/ fingernail, gray, brown, green, (talc) Soapstone Basalt, Gabbro or Ultramafic Igneous Rocks Microcrystalline or coarser crystalline texture Light colored effervesces with dilute HCl (calcite, dolomite) Marble Limestone or Dolostone Sandy texture Various colors, pink, usually white to gray, sandy texture that is fused together, (Quartz) Quartzite Sandstone Coarse grained, various sizes like conglomerate Larger grains/pebbles may be stretched, various colors Meta- conglomerate Conglomerate