1. Substances composed of minerals.

2. Rocks are made from many minerals, so we CANNOT test properties!
Instead, rocks are defined by HOW they form (Environment of
Formation).

3. Let’s start with Igneous Rocks…

4. Form from solidified lava or magma.
Igneous Rocks
Form from solidified lava or magma.

6. The flowchart below illustrates the change from
lava to the extrusive rock basalt.
The solidification of the melted rock occurred
(1) slowly, underground
(2) slowly, above ground
(3) rapidly, underground
(4) rapidly, above ground

7. Intrusive - Cools slowly underground
Coarse (big) Crystals
Extrusive – Cools quickly above ground Fine (small) or Glassy (no crystals).
Sometimes Vesicular (“catches gas”)

8. The flowchart below illustrates the change from melted rock to basalt.
The solidification of the melted rock occurred
(1) slowly, resulting in fine-grained minerals
(2) slowly, resulting in coarse-grained minerals
(3) rapidly, resulting in fine-grained minerals
(4) rapidly, resulting in coarse-grained minerals

9. light-colored metamorphic fine-grained igneous
In addition to ash,
solid rock formed on
Mt. Hekla from the
lava extruded during
an eruption. This
rock is most likely
Mt. Hekla
light-colored metamorphic
fine-grained igneous
(3) dark-colored metamorphic
(4) coarse-grained igneous

10. MAFIC
FELSIC

11. Which igneous rock is probably best described as being
non-vesicular and mafic?
(1) andesite (3) gabbro
(2) pegmatite (4) obsidian

12. Which graph best represents the relative densities of three different types of igneous rock?

13. Which INTRUSIVE rock is approximately 30% Amphibole ?
(1) granite (3) basalt
(2) andesite (4) diorite

15. What is the approximate % of Plagioclase Feldspar in a typical Andesite?
≈55%

16. How about the approximate % of Biotite in a very FELSIC sample of Andesite?
≈ 18 %
≈ 8 % for a Mafic sample

17. (1) granite (2) rhyolite (4) basalt (3) gabbro
Which intrusive igneous rock could be composed of approximately 60% pyroxene, 25% plagioclase feldspar, 10% olivine, and % amphibole?
(1) granite
(2) rhyolite (4) basalt
(3) gabbro