Substances composed of minerals.

Rocks are made from many

minerals, so we CANNOT test properties!

Instead, rocks are defined by HOW they form (Environment

ofFormation).

Let’s start with Igneous Rocks…

Igneous Rocks

Form from solidified lava or

magma.

The flowchart below illustrates the change fromlava 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

Intrusive - Cools slowly underground Coarse (big) Crystals

Extrusive – Cools quickly above ground Fine (small) or Glassy (no

crystals). Sometimes Vesicular (“catches

gas”)

The flowchart below illustrates the change frommelted 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

In addition to ash, solid rock formed on Mt. Hekla from the lava extruded during an eruption. This rock is most likely

(1) light-colored metamorphic (2) fine-grained igneous(3) dark-colored metamorphic (4) coarse-grained igneous

Mt. Hekla

MAFICFELSIC

Which igneous rock is probably best described as being non-vesicular and mafic?

(1) andesite (3) gabbro

(2) pegmatite (4) obsidian

Which graph best represents the relative densities of three different types of igneous

rock?

Which INTRUSIVE rock is approximately 30% Amphibole ?

(1) granite (3) basalt

(2) andesite (4) diorite

What is the approximate % of Plagioclase Feldspar

in a typical Andesite?

≈55%

How about the approximate % of Biotite in

a very FELSIC sample of Andesite?

≈ 18 %

≈ 8 % for a Mafic sample

Which intrusive igneous rock could be composed of approximately 60% pyroxene,

25% plagioclase feldspar, 10% olivine, and 5% amphibole?

(1) granite (2) rhyolite (4) basalt

(3) gabbro