Name __________________ Petrology — Spring 2006 Igneous rocks lab — Part IV Hand samples vs. thin sections 1 — Complete a sample description sheet for each of the below thin sections. At minimum, identify all minerals present, estimate the modal percentages of each mineral, and describe the texture: 6 — 8 — 13 — 21 — 24 — 25 — 29 — 30 — 31 2 — Using the appropriate IUGS igneous rock classification diagram, name the rock. 3 — Determine which hand sample from “Igneous rocks lab — Part II” corresponds to each thin section. Write the hand sample number next to the thin section number on your sample description sheet. 4 — Write a detailed hand sample description on your sample description sheet in the appropriate field. Here are some examples: Dark gray, coarse-grained plutonic rock Buff-colored porphyritic volcanic rock with mm-size quartz phenocrysts Aphanitic volcanic rock with a glassy texture containing large (~1 cm) feldspar phenocrysts 5 — Thinking problems (nothing to write down or turn in, but please consider): How accurately were you able to identify the rock using only the hand sample (as you would need to do in the field)? What information did you get (or could have gotten) from looking at the thin sections that you couldn’t know from just looking at the hand samples? How useful is the color index of the rock in identifying the rock? Why is it important to consider color when examining a rock? Why is color not completely reliable when identifying a rock? What else would a petrologist need to know about a rock (and the minerals within the rock) to classify it completely? How would a petrologist get that information? Who cares? Why identify rocks at all? Seriously — Why? Don’t know the answers to these questions? Let’s discuss.Sample Number(s)Locality:Sketches of key relationsRock name:Field or hand-specimen description:MINERALOGY: Name Modal % Optical properties/CompositionMajor phases:Accessory:TEXTURES/STRUCTURES:PETROGENESIS/INTERPRETATION:IGNEOUS - METAMORPHIC - SEDIMENTARY(circle one)Sample Number(s)Locality:Sketches of key relationsRock name:Field or hand-specimen description:MINERALOGY: Name Modal % Optical properties/CompositionMajor phases:Accessory:TEXTURES/STRUCTURES:PETROGENESIS/INTERPRETATION:IGNEOUS - METAMORPHIC - SEDIMENTARY(circle
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