Lab I: Hand Sample Description & IUGS Classification Schemes
Purpose
In this lab, you will have the opportunity to refine your observational skills and build your petrographic vocabulary through construction of detailed rock descriptions. You will increase your familiarity and proficiency with igneous rock classification schemes. You will develop a more complete appreciation for the accuracy and precision achieved during point counting.
Preparation
Please read all of Chapter 2 and pages and pages 67-76 in Chapter 3 (IUGS classification scheme) prior to coming to lab.
In addition, refresh your memory of the definitions of the following terms. Most of these terms are discussed in Chapter 2.
Degree of CrystallinityGrain Size
- Holocrystalline
- Hypocrystalline
- Holohyaline
Grain Size Distribution
- aphanitic
- phaneritic
- microlites
- crystallites
- fine-grained
- medium-grained
- coarse-grained
- very coarse-grained
- megacrysts
- pegmatite
Grain Shape
- equigranular
- inequigranular
- seriate
- porphyritic (bimodal, trimodal; be sure to describe the distinct populations separately)
- glomeroporphyritic
- microporphyritic
Additional textural terms
- euhedral
- subhedral
- anhedral
- graphic, micrographic
- granophyric
- vermicular
- mantle, corona, rapakivi & antirapakivi
- poikiolitic
- trachyitic
- vesicular