Igneous Rock Lab

Assignment: Activity 6, pg 96. Activity 8, complete Igneous Rock Worksheet, pg 98. For the Bowen's reaction series column list if the temperature of cooling was high, medium or low.


Igneous Rock Textures

Texture depends on the _______ of cooling.

  • Magma- molten rock material __________ the earth's surface.
  • Lava- molten rock material which has reached the ________ of the earth.

Intrusive igneous rocks- those rocks which cool and crystallize ________ beneath the earth's surface from magma, forming mineral crystals large enough to be seen.

  • Phaneritic (coarse grained) rocks have mineral crystals that are ______ enough to be seen without __________.
  • Pegmitites- very course grained felsic rock. Crystals are generally larger than ____ cm in diameter.

Extrusive igneous rocks- those rocks which cool and crystallize _________ at the earth's surface from lava forming mineral crystals too small to be seen.

  • Aphanitic (fine grained) rocks have mineral crystals that are too ________ to be seen without magnification.

Porphyry- rocks containing more than one mineral crystal ________. The large, visible minerals are called phenocrysts and the fine grained materal surrounding them is called the _____________. An aphanitic porphyry has a fine grained matrix such as a rhyolite porphyry. A rock with two different sizes of coarse grained rock is called a phaneritic porphyry as in a granite porphyry.

Vesicular/Porous- the presence of _________ cavities (gas bubbles) in a rock. These gas bubbles are called ________. In felsic rocks, these gas bubbles are often small, taking on a frothy appearance. The rock may even float in water as in ________. In mafic rocks, the gas bubbles are typically larger and more prominent, making the rock look more like a __________. ex. scoria.

Amygdaloidal- vesicles (air holes) in a rock which are later filled in with _________. These former gas bubbles, now filled, are called amygdules. Hint: crystals are never ________ naturally!

Glassy- term given to a rock which solidified so quickly from its molten state such that ______ crystals were able to form. ex. ___________


Igneous Rock Colors

The minerals which make up an igneous rock determine its _______.

Mafic- rocks resulting from molten material whose composition is relatively ______ in silica and feldspar but high in magnesium and _________.

  • Because most of the mafic rock forming minerals (_____-rich plagioclase, amphibole/hornblende, olivine, biotite, pyroxene, etc.) are dark in color, the resulting rock tends to be _______ in color.

Felsic- rocks resulting from molten materal whose composition is relatively high in ______ and aluminum but low in ferromagnesians.

  • Since most of the felsic rock forming minerals (_________, potassium-felspar, muscovite, na-rich plagioclase, etc.) are light in color, the resulting rock tends to be ______ in color also.

Rocks containing roughly the same amounts of both light and dark colored minerals are said to be ____________ in color.


Other Igneous Rocks

Pyroclastic- rock material ejected from ________- type volcanoes.

Tuff- rock fromed from volcanic _______.

Syenite- a granitic rock (coarse-grained, felsic) but lacking _____.


Bowen's Reaction Series

  • High Temperature- _______ colored minerals
  • Medium Temperature- intermediate colored minerals
  • _______ Temperature- lighter colored minerals