Lab 1: Hand Specimens of Metamorphic Rocks

12.109 Lab 11 17 Nov., 2005 Due 29 Nov., 2005 Lab 11: Hand Specimens of Metamorphic Rocks The purpose of this lab is to begin to familiarize you with metamorphic rock types and what they look like in hand sample. It is also to get you to practice naming metamorphic rocks and thinking about the effect of composition and metamorphic grade on mineralogy. It is not an exciting lab in concept, but the rocks are pretty, and contain minerals which are very important in metamorphic petrology, so engrain them into your psyche. The ultimate goal, of course, is for you to learn how to identify these rocks in the field. If you are uncertain whether an unknown mineral is one thing or another, write down what it is that makes the identification uncertain. Here is a list of the minerals you might see along with a brief, incomplete, and ambiguous description. Use your other resources to get more information: quartz- if you can't identify this, you fail apatite- distinct basal parting and hexagonal mineral habit plagioclase- white, a little glassy biotite- black, thin sheets muscovite- silvery white, thin sheets tremolite- long clear prisms staurolite- short black crystals, look for twinning andalusite- square cross section, chiasolite crosses, elongate crystals kyanite- pearly luster, bluish--kyanite’s hardness varies dramatically with direction: H=5 parallel to the length of the crystal, H=7 across the length. Conveniently, steel is around H=6... sillimanite- pearly luster, square cross section stilpnomelane - like biotite, only the habit is distinctively different chlorite- green, thin sheets tourmaline- long black prismatic crysals, dintinct luster, striations and habit in crosssection chloritoid- black, dark grey, euhedral crystals--usually present as porphyroblasts graphite- gray, greasy appearance pyroxene- typically black, omphacite is green glaucophane/riebekite- blueish amphiboles calcite- variable color, use hcl, 3 perfect cleavage directions, soft (H=3) pyrite- looks like gold, little cubes serpentine- green, dark green, platy/fibrous garnet- red (Fe, Mg varieties) or orange (Ca), soccer ball shape hornblende- long black crystals, look for cleavage angle (not crystal habit) epidote- pistachio green color, association zoisite/clinozoisite- difficult to tell from plagioclase. Association may be the only way 1 12.109 Lab 11 17 Nov., 2005 Due 29 Nov., 2005 S/M Rock Type? Protolith? Observe the relict bedding (S0) and the metamorphic foliation (S1). For those in the structure class, sketch the specimen as if it were in a fold, assuming that the metamorphic foliation is an axial planar cleavage. 22 What are the minerals in this rock? Name the rock What is the protolith? What metamorphic facies would you put it in? 126 Frederick County, Maryland. Name the rock Protolith? What metamorphic mineral is present? (hint: it gives this rock its color) 145 Greenville Rock Type? What metamorphic mineral is present? What was the original rock type? If this rock was collected above water, what tectonic environment was it likely metamorphosed in? 38-30 Bethel, Vermont. Identify and describe 3 metamorphic minerals. Rock name? Protolith? 2 12.109 Lab 11 17 Nov., 2005 Due 29 Nov., 2005 N-1 What is the porphyroblast? What are the other minerals? What is the bulk composition? What is the rock name? What is its metamorphic grade? 2027 Rock type? Protolith? Can you tell what P/T conditions this rock made it up to? 1944 What are the 3 dominant minerals in this rock (hint: one of them is graphite, and one of them is really not obvious at all) Which of the minerals occur as porphyroblasts? Rock name: MS-31 Mendocino, CA The black platy mineral looks very much like biotite, but is not, what is it? Describe its crystallization in regard to the main fabric development. Name 2 other phases in this rock. Name the rock. GS-1 Zermatt, Switzerland Name and describe 3 prominent phases. Name the rock. Protolith What tectonic environment was this sampled in? 3 12.109 Lab 11 17 Nov., 2005 Due 29 Nov., 2005 M Name the rock. What is the protolith? What grade of metamorphism is this rock? 757 Rock type? Is this classification based primarily on composition or texture? 1348 Identify the prominent porphyroblast phase What other minerals are in this rock? Protolith 1261 Identify and describe 3 prominent phases. Describe the texture. Speculate on the genesis of this rock. 93 Name principle phases Name the rock. What is the protolith? What metamorphic grade is this stuff? 80 What are the principal phases? Name the rock. What is a likely protolith? 307 What's the mineralogy? Name the rock. 4 12.109 Lab 11 17 Nov., 2005 Due 29 Nov., 2005 6261 What phases are present? Name the rock. (e.c.: does this rock show shear banding or S-C fabric? What is the sense of shear?) 5224625 What are the minerals? What is the protolith? What would you name the rock? BF02 This is the highest grade sample in the lab, and records pressures of up to 1-1.2 GPa and temperatures in excess of 800 ˚C. How kilometers depth is that? What metamorphic grade is that? What do you think the prograde mineralogy is? This rock is retrogressed a bit. What is the retrograde assembly? Name that rock. F03 This rock is like BF02, but instead, it is more thoroughly retrogressed. Can you tell in handsample? Name this rock too. 5