1. What are Igneous Rocks???? Form when magma cools and minerals crystallize

2. Composition of magma Type of Igneous rock depends on the composition of the magma – Silica is the most abundant compound and has the greatest effect on magma characteristics 3 classifications of magma based on the amount of silica it contains – Basaltic – Andesitic – Rhyolitic

3. Chemical composition of lava is a little bit different than the magma it came from – Dissolved gases escape into the atmosphere

4. Magma Formation Two ways of formation – Melting earth’s crust – Melting within the mantle Four factors – Temperature Increases with depth within earth’s crust Geothermal gradient – Pressure Also increases with depth Result of the weight of overlying rock Pressure increases, melting point increases

5. – Water content Changes the melting point of the rocks Water content increases, melting point decreases – Mineral content Different minerals have different melting points Basalt – high melting point Granite – lower melting point – Contains more water Rocks high in iron and magnesium – high melting point Rocks high in silicon – low melting point

6. Partial Melting Process whereby some minerals melt at relatively low temperatures while other minerals remain solid – New elements are added during the process Changing the chemical composition One way different types of igneous rocks are formed

7. Bowen’s Reaction Series: minerals form in predicatable patterns

8. Bowen’s Reaction Series – Iron- rich minerals (left side) Go through abrupt changes as magma cools – Feldspars (right side) Lighter minerals Continually change chemical composition as magma cools

9. Classification of Igneous Rocks Intrusive rocks – Magma cools and crystallizes below the earth’s crust Magma injected into surrounding rock

10. Extrusive rocks – Cools and crystallizes on the Earth’s surface – Lava flow of flood basalts – Classified by: Mineral composition Physical properties – Grain size – texture

11. Classification of Igneous rocks Based on mineral compositions – Basaltic Dark colored Lower silica content – Granitic rocks Light colored High silica content – Intermediate Falls between basaltic and granitic Feldspar and hornblende – Ultrabasic Contain only iron rich minerals Always dark

12. Basaltic Gabbro

13. Granitic granite

14. Intermediate Feldspar Hornblende

15. Ultra basic Pyroxene

16. Crystal size and cooling rates When lava cools on the earth’s surface – Cools quickly – Not enough time for large crystals to form Rhyolite – hard to see crystals without magnification – Sometimes no crystals form When magma cools beneath earth’s surface – Cools slowly – Large crystals form

17. Porphyritic Rocks Porphyritic texture Large crystals surrounded by finer crystals of same or different minerals – Complex cooling First – slow cooling – big crystals Then quicker as the magma moves closer to the earth’s surface (or erupted onto the surface) – small crystals porphyritic granite

18. Vesicular rocks Vesicular texture – Big holes making the rock look spongy Dissolved gases escape when pressure lessens Leaving vesicles behind

19. Thin sections Easier to observe igneous rock composition when viewed in a thin strip under a microscope hornblende olivine

20. Igneous rocks in resources Veins – Fluid left during magma crystallization contain high levels of water, silica, and leftover minerals – Fluid fills in the cracks of surrounding rocks – Solidifies into mineral-rich quartz veins

21. Pegmatites Veins of very large-grained minerals Ores of rare elements form Can produce beautiful crystals

22. Kimberlites Veins in ultrabasic rock Diamonds Most likely form deep in the crust or mantle – Intrude quickly upward – Forming long, narrow, pipe like structures

23. Obsidian Normally extrusive Forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. The result is a volcanic glass with a smooth uniform texture that breaks with fracture

24. Rhyolite Light-colored Fine-grained Extrusive igneous rock Typically contains quartz and feldspar minerals.

25. Biotite Granite intrusive, most commonly occurring in batholiths

26. Hornblende greenish-black to black extrusive

27. Basalt Basalt is dark-colored and fine-grained extrusive

28. Gabbro Gabbro is dark, medium- to coarse-grained Intrusive igneous rock