Physical Geology Helpful Lab Hints

Exercise 3: Igneous Rocks

• The Rocks (click here for the rocks you need to identify)
• Use the Table on page 42 in your lab book
  • for an annotated version, click here
  • The rock names are based on mineral composition and texture (discussed below).
  • Note that there are six rock names on the chart: granite (circled), diorite, gabbo, rhyolite, andesite, and basalt.  Those six names may be modified with a more specific texture term.
• Identify the mineral composition of the rock.
  • Use the descriptions on page 38-39.
  • Remember: the color of the rock reflects the minerals present
    • Felsic rocks contain potassium feldspar (pink), quartz (clear) and some Na-plagioclase feldspar (white)
    • Intermediate rocks contain Na- & Ca-plagioclase feldspars (white to dark grey), hornblende (black), biotite (black), and augite (black)
    • Mafic rocks contain Ca-plagioclase feldspar (dark grey), augite (black), and olivene (dark green)
    • Ultramafic rocks contain olivene (dark green) and augite (black)
  • If you can see mineral crystals, try to identify them based on the overall composition of the rock. For example, if the rock is felsic, you may be able to observe quartz, potassium feldspar, Na-plagioclase feldspar and even a few specks of hornblende, biotite or muscovite.
• Identify the texture of the rock.
  • Use the descriptions on pages 37 & 38.
  • Use this flow chart to assist you.
• Use the chart on page 42 in the lab book to identify the rock using the mineral composition and the texture.
  • The linked chart is annotated to indicate which rows are Intrusive and which are Extrusive

Igneous Rock ID: A Practical Online Study Guide

Back to lab help.

GEL 1008 | courses | office hours | Mike's Home | IVCC Home | Contact IVCC | Contact Mike

copyright © 2020 Mike Phillips (includes all photos)
last updated: 2021-01-25