Smith Brandon GEOG 1403, 2/17/09
1403 Online Lab 6 Metamorphic Rocks Ch-5: P. 79-87 PLEASE CHOOSE A FONT COLOR OTHER THAN BLACK FOR YOUR ANSWERS Read pages 79-87 in your lab manual very carefully. Have your common rocks set available see metamorphic samples. Answer the following problems:
1. Define metamorphic rock:
Metamorphic rock s are crystalline rocks that form from other rocks.
2. Metamorphic rocks are subdivided into two major textural groups: FOLIATED and
NONFOLIATED. Divide metamorphic samples into these two categories. a. Foliated: Gneiss, Slate, Mica-Schist b. Nonfoliated: Quartzite, Serpentine, Marble 3. Many foliated metamorphic rocks form by the metamorphism of shale; the more intense (or higher grade) the metamorphism, the coarser the crystals contained in the rocks. a. Select from among your samples that may have been derived from shale, and arrange them according to metamorphic grade (see Table 5.2) Lowest grade: Slate Intermediate grade: Quartzite (has a varying metamorphic grade), Mica-Schist, Marble (has a varying metamorphic grade), Serpentine (has a varying metamorphic grade) Highest grade: Gneiss
4. Assuming that the rocks you selected formed in the vicinity of a magmatic zone at a
convergent plate boundary, what were the approximate temperatures and depths of each grade at the time of metamorphism (see Fig. 5.1) Lowest Grade: 200 to 320 degrees Celsius, with a pressure of 300 to 600 MPa Intermediate Grade: 320 to around 520 degrees Celsius, with a pressure of 600 to 1000 MPa Highest Grade: Greater than 520 degrees Celsius, and pressure of over 1000 MPa 5. How can you distinguish between the following similar-looking rocks? a. Marble and quartzite: Quartzite is harder and will scratch glass. Marble will not. Marble made is of calcite or dolomite, or both, and quartzite is made of quartz. The crystals of these three minerals have different shapes, and the quartz crystals are shinier. b. Slate and phyllite: The degree of metamorphism is different between slate and phyllite. Phyllite is slate further metamorphosed. c. Schist and gneiss: Both Schist and Gneiss are foliated metamorphic rocks in which individual minerals can be seen with by the naked eye. The difference is that Gneiss is generally more coarsely crystalline and has color banding, unlike Schist. 6. Examine your metamorphic rock samples and fill out the chart below
Brandon Smith GEOG 1403, 2/17/09 Sample Grain Size Number & (coarse, medium, fine) Rock Name
Mineral Composition
Texture
(foliated or nonfoliated)
Parent Rock
Shale, Mudstone, Granite
Reacts w/acid
Formation History
(contact/regional/grad e of metamorphism)
Gneiss
Slate
Mica-Schist
Coarse Grained Quartz, Foliated Potassium Feldspar, Sodium Feldspar Fine Grained Quartz, Foliated Muscovite, Biotite, Chlorite, Hematite, Pyrite Medium Quartz, Foliated Grained Potassium Feldspar Fine Grained Magnesium, Iron, Aluminum, Nickel Non-Foliated
No
High grade, gneissic foliation, light and dark layers common Low grade, slaty cleavage, generally dark Intermediate grade, schistose foliation Varying metamorphic grade, greenish color, commonly mottled or streaked Varying metamorphic grade, crystalline
Variable metamorphic grade, effervesces to dilute HCl, commonly coarsely crystalline
Shale or Mudstone
No
Shale or Mudstone Peridotite
No
No
Serpentine
Coarse Grained Quartz Quartzite Medium Grained Calcite
Non-Foliated
Quartz Sandstone
No
Non-Foliated
Marble
Limestone or Dolostone
Yes
Brandon Smith GEOG 1403, 2/17/09