- A. There are three types of rocks-igneous, sedimentary, and metamorphic
- B.The rock cycle shows the relationshi[s between the three types of rocks and how one type of rock may give rise to a different type of rock
Igenous Rocks- Fire formed
- 1. Magma-molten rock within the earth
- a.Intrusive igneous rocks form from magmas
- 2. Lava-molten rock that erupts on the earths surface
- a. Extrusive igneous rocks form from lavas
- 3.Both magma and lava may be composed of solids, liquids, gases.
- 4. As magmas and lavas cool, minerals cystallize and grow until they the edges of other minerals, so igneous rocks are composed of interlocking minerals
- 5.Ignous rocks are classified according to their texture and composition
Igneous Rock Textures-Size, Shape, Araangement of Minerals
- A. Coarse-grained (Phaneritic) texture
- 1.All of the minerals are about the same size and are visisble to the naked eye
- 2.Phaneritic texture develops because magma cools slowly
- a.The surrounding rocks don't conduct heat well, so magmas may stay hot
- for long periods of time thus giving minerals time to grow larger.
- B.Fine grained (Aphanitic) texture
- 1. All of the minerals are about the same size but are too small to see with the naked eye
- a.Aphanititc texture develops when lavas cool quickly
- i.Many small minerals develop, but lava cools so quickley there is no time for minerals to grow large.
- C.Porphyritic Texture
- 1.Minerala are of two sizes due to different rates of cooling.
- a. Phaneritic- porphyritic texture
- i. All minerals are visible, but some minerals are significantly larger.
- b. Aphanitici-porphyritic texture
- i. larger minerals in a matrix of smaller minerals.
- ii. Slow rate of cooling then fast rate of cooling
- a. some minerals formed from magmas as it slowly cooled the magma erupted onto the surface and cooked quickly
- D. Glassy texture
- 1. Lava cools instantly, no minerals are present
- 2. Obisidian (volcanic glass)
- 3.Pumice- light colored
- 4.Scoria- dark colored
- E. Pyroclastic texture
- 1.Pyroclastic material forms when material is ejected explosively during a volcanic eruption.
- 2. Range from dust and ash (very small) to lapilli and bombs
- 3.Pyroclastic materials consolidate to form igneous rocks with pyroclastic textures
Igneous Rocks Compositions
- A. Bowens Reaction Series
- 1.Bowen experimented how minerals cyrstallize from a magma
- 2. As magma cools, minerals crystallize
- 3.Different minerals cyrstallize at different temperatures
- 4. Ideally, when a magma cools the first mineral to cyrstalliize is olivine, the last to cyrstallize is quartz
- 5. Minerasl that crystalize at about the same temperature are found togethere in the same igneous rock
Classification of Igneous Rock
- A.Felsic(granitic) composition
- 1.Rocks that are composed mostly of light colored minerals such as quartz and feldspar