Name _______________________ Petrology — Spring 2006 Optical mineralogy lab — Part I Due Thursday 2/9 Mineral properties identifiable in plane polarized light Color, pleochroism, relief, cleavage, and crystal habit are only/best observed in plane polarized light. Answer the questions below to familiarize yourself with these optical mineral properties. Color 1 — Choose two thin sections (number 8, 32, 76 or 99) and look at them in plane polarized light. Describe the colors of the minerals you see. Mineral 1: Mineral 1: Mineral 2: Mineral 2: Mineral 3: Mineral 3: Mineral 4: Mineral 4: Mineral 5: Mineral 5: Pleochroism 2 — In the thin sections you choose for Question 1 above, you should have noticed at least one mineral that exhibits pleochroism; describe how the color changes in any pleochroic minerals you see as you rotate the stage. Mineral 1: Mineral 1: Mineral 2: Mineral 2: Relief 3 — Evaluate the relief of the minerals in two thin sections (1, 76, 82 or 100). Compare the relief of the minerals you see and estimate the percentage of each different phase you observe (you should be able to distinguish between the major phases. Mineral 1: Mineral 1: Mineral 2: Mineral 2: Mineral 3: Mineral 3: Mineral 4: Mineral 4: Mineral 5: Mineral 5: Thin section: Thin section: Thin section: Thin section: Thin section: Thin section:Name _______________________ Petrology — Spring 2006 Cleavage 4 — Describe the cleavage of the minerals in the two thin sections you chose to evaluate relief. Cleavage may also be seen in crossed polarized light; look at these minerals in XPL to see if cleavage is more easily seen. Mineral 1: Mineral 1: Mineral 2: Mineral 2: Mineral 3: Mineral 3: Mineral 4: Mineral 4: Mineral 5: Mineral 5: Crystal Habit 5 — Describe the habit of minerals from any two thin sections you’ve already looked at. Crystal habit may also be seen in crossed polarized light; look at these minerals in XPL to see if their habit is more easily seen. Mineral 1: Mineral 1: Mineral 2: Mineral 2: Mineral 3: Mineral 3: Mineral 4: Mineral 4: Mineral 5: Mineral 5: Mineral properties identifiable under crossed polars Interference colors (or birefringence) and mineral extinction are two properties that are observed under crossed polars. Birefringence 6 — Evaluate the birefringence of quartz in thin section number 32 or 78 – Find a mineral with first order birefringence and undulatory extinction. Describe the interference colors you see and the characteristics of quartz as you rotate the stage. Thin section: Thin section: Thin section: Thin section:Name _______________________ Petrology — Spring 2006 Birefringence, continued... 7 — Insert the upper polarizer to observe birefringence in two of the following thin sections (8, 76, 99 or 100). The standard thickness for a thin section is 30 µm; describe the interference color and write down the birefringence. Mineral 1: Mineral 1: Mineral 2: Mineral 2: Mineral 3: Mineral 3: Mineral 4: Mineral 4: Mineral 5: Mineral 5: Extinction 8 — Isotropic vs. anisotropic minerals. Choose either thin section 99 or 100 and look for isotropic minerals. Describe what it/they look like in PPL and XPL. Mineral 1: Mineral 2: Mineral 3: 9 — Extinction angle. Choose any thin section you’ve already looked at that contains one or minerals with a well-defined cleavage. Determiner whether you see parallel or inclined extinction; if you see inclined extinction, what extinction angles do you find for these minerals. Mineral 1: Mineral 2: Mineral 3: Thin section: Thin section: Thin section: Thin section:Name _______________________ Petrology — Spring 2006 Review 10 — Choose any thin section from the class collection and describe it using all the mineral properties we’ve discussed today. Estimate the percentages of the various mineral phases you see (you total should add to 100%). Thin