Igneous Rocks
1. Pegmatite
2. Granite
3. Syenite
4. Anorthosite
5. Gabbro
6. Rhyolite Porphyry
7. Trachyte Porphyry
8. Basalt
9. Rhyolite
10. Andesite
11. Tuff
12. Obsidian
13. Pitchstone
14. Pumice
15. Scoria
IGNEOUS ROCK QUESTIONS:
(1) INTRUSIVE/EXTRUSIVE pairs:
GRANITE FAMILY (felsic): Granite (#2) and Rhyolite (#9)
GABBRO FAMILY (mafic): Gabbro (#5) and Basalt(#8)
How can you tell intrusive vs. extrusive rocks apart? How can you tell these two
different igneous rock families apart?
(2) What is obsidian (#12) and how does it form?
(3) Pegmatite (#1) has a similar composition as granite(#2). What differences can
you SEE between these two rocks? What does that tell you about how fast/slow
pegmatite forms compared with granite?
(4) Tuff (#11) consists of compacted volcanic fragments from explosive eruptions.
Looking at the rock (especially its texture), what gives you hints of this explosive
origin?
(5) Scoria is mafic and Pumice is felsic. Both have gas holes. What are two ways to
tell the difference between these two rocks?
Sedimentary Rocks
1. Conglomerate
2. Arkose
3. Sandstone
4. Quartz Sandstone
5. Oil Shale
6. Shale
7. Breccia
8. Limestone
9. Gypsum
10. Fossil Limestone
11. Dolomite
12. Tufa
13. Rock Salt
14. Chalk
15. Bituminous Coal
Sedimentary:
(6) What distinctive features can you use to tell apart the different clastic
sediments: Conglomerate (#1) vs. Sandstone (#3 or 4) vs. Shale (#5 or 6)?
(7) Can you tell the difference between oil shale (#5) and regular shale (#6) by
smell? (lightly scratch the rocks before you smell them)
(8) Sedimentary rocks can give clues as to where they were formed. Sandstone
sample #4 clearly shows bedding. The fossils in the Limestone # 10 are tiny or
broken, but still visible. Sketch these sedimentary features.
(9) SAME BASIC COMPOSITION, DIFFERENT FORMATION: CALCIUM CARBONATE
Tufa (#12) is precipitated, usually from hot springs, and limestone (#8) is also
precipitated. Fossiliferous limestone (#10) contains visible fossils, and chalk
(#14) is made from microscopic skeletons of plankton (microscopic fossils).
(a) COMPARE Limestone (#8) and Fossiliferous Limestone (#10):
What is different? What does that tell you about how they were formed? Which
is considered “Chemical” and which is considered “organic”?
(b) Chalk also contains fossils, but they are microscopic. Is this a chemical or
biological rock? What about chalk is unique and will help you identify it?
Metamorphic Rocks
1. Gneiss
2. Graphite Schist
3. Mica Schist
4. Chlorite Schist
5. Garnet Schist
6. Slate
7. Amphibolite
8. Talc Schist
9. Phyllite
10. Quartzite
11. Serpentine
12. Marble
13. Serpentine Marble
14. Hornfels
15. Anthracite
METAMORPHIC ROCKS:
(10) Foliated Rocks: #6 => #9 => #3 => #1: are a series from lowest to highest
metamorphic grade. Sketch the foliated texture of these four rocks. How does the
texture change as you increase grade? Name one distinctive feature about each rock
that will help you tell them apart.
(11) Serpentinite (#11). What is the distinctive color of this rock? It comes from the
mineral serpentine. The parent rock typically is ultramafic. What color are
ultramafic igneous rocks?
(12) Both hornsfels (#14) and Schist (#3) are metamorphosed clastic sediments.
How is the texture of these two rocks different? What does that tell you about
regional vs. local metamorphism?
PARENT SEDIMENTARY ROCK – METAMORPHIC ROCK PAIRS:
How are they alike? How can you tell them apart?
(13) #15 Bituminous Coal (Sed) and #15 Anthracite (Meta)
(14) #6 shale (Sed) and #6 slate (Meta)
(15) #8 limestone (Sed) and # 12 Marble (Meta)
(16) #3 or 4 Sandstone (Sed) and #10 Quartzite (Meta)