1. Unit 3 - Rock Types Igneous Rocks

2. Basic Rock Classifications ● Igneous ● Sedimentary ● Metamorphic

3. Igneous Rocks An igneous rock is formed when magma or lava cools and solidifies Molten rock in the Earth is magma  Magma is buoyant, rises to surface, & sometimes breaks through Magma reaches Earth’s surface it is called lava

4. Igneous Rocks Two types of igneous rocks ● Plutonic/Intrusive – cools underground ● Volcanic/Extrusive – cools above ground

5. Plutonic rocks To see them, they must be uplifted to surface And softer surrounding rock eroded away

6. Plutonic rocks Volcanic necks Shallow intrusion formed when magma solidifies in throat of volcano

7. Plutonic rocks Dikes Tabular intrusive structure that cuts across any layering in existing rock

8. Plutonic rocks Sills Tabular intrusive structure that parallels layering in existing rock

9. Plutonic rocks Plutons Large, blob-shaped intrusive body formed of coarse- grained igneous rock, commonly granitic Small plutons are called stocks, large plutons are called batholiths

10. Geothermal Gradient – the rate at which temperature increases with depth in the Earth *important for the formation of igneous rocks

11. Igneous Rock Formation As magma cools, atoms arrange in an orderly crystal structure crystallization

12. Igneous Rock Classification Igneous rocks are classified two ways 1. Texture 2. Mineral composition

13. Igneous Rock Classification - Texture

15. 5 Types of Textures 1. Phaneritic (coarse-grained) 2. Aphanitic (fine-grained) 3. Glassy (compact and frothy) 4. Vesicular 5.Porphyritic

16. Textures - Phaneritic (coarse-grained) forms far below surface Slow Cooling Large Crystals Examples: Gabbro, diorite, and granite

17. Textures - Aphanitic (fine-grained) fast cooling magma/lava forms at or near surface can’t see individual crystals (small) Examples: Basalt, andesite, and rhyolite

21. Texture - Glassy (compact and frothy) Very Rapid Cooling No Crystal Structure Example: Obsidian

22. Texture - Vesicular Has many cavities at its surface and inside Forms from gas bubbles in the magma Example: Pumice * Can be aphanitic vesicular or glassy vesicular rocks

23. Texture - Porphyritic 2 cooling stages: magma cooled slowly for a while then erupted and cooled quickly. minerals crystallize at different temperatures and or rates Different sized crystals Example: Porphyritic Granite

24. Worksheet - Homework Igneous Rock (Texture) Worksheet

25. Igneous Rock Classification Igneous rocks are classified two ways 1. Texture 2. Mineral composition

26. Igneous Rock Classification - Chemical Composition mainly silicate minerals determined by composition of magma from which it crystallized magma mainly 8 elements: Si, O, Al, Ca, Na, K, Mg, Fe Al - light coloured Mg - dark coloured

27. Bowen's Reaction Series The geologist N.L. Bowen (Norman) found that minerals tend to form in specific sequences in igneous rocks These sequences are assembled into temperature gradient chart

28. Bowen’s Reaction Series

29. Igneous Mineral Composition Types 1. Mafic 2. Felsic 3. Intermediate 4. Ultramafic

30. Igneous Mineral Composition Types - Mafic Have ~50% silica, by weight, Contain dark colored minerals with iron, magnesium and calcium Examples: Intrusive/extrusive - gabbro/basalt

31. Mafic Chemical Composition

32. Igneous Mineral Composition Types - Felsic Have >65% silica, by weight, Contain light-colored minerals that are abundant in silica, aluminum, sodium and potassium Examples: Intrusive/extrusive - granite/rhyolite

33. Felsic Chemical Composition

34. Igneous Mineral Composition Types - Intermediate rocks have silica between (50-65%) those of mafic and felsic rocks Examples: Intrusive/extrusive - diorite/andesite

35. Intermediate Chemical Composition

36. Igneous Mineral Composition Types - Ultramafic Have the least amount of <45% silica, by weight, Are composed almost entirely of dark-colored ferromagnesian (Fe and Mg) minerals Example: peridotite (intrusive)

38. Special Note Different minerals crystallize from magma at different temperatures. (Bowen’s Reaction Series) As minerals crystallize from magma the remaining composition is forever changed. Therefore, it is possible for more than one igneous rock to form from the same magma depending on the cooling environment.

39. Worksheet - Homework Igneous Rock (Composition) Worksheet

40. Diamonds STSE - Kimberlite What is a kimberlite? kimberlite is a ultramafic, igneous rock which occurs as small volcanic pipes, dykes, and sills. Kimberlite commonly contains inclusions of ultramafic rocks.

41. Kimberlite and Diamonds they are formed deep within the mantle, at are erupted rapidly and violently, It is this depth of melting and generation which makes kimberlites prone to hosting diamond xenocrysts.

44. Kimberlite indicators formed under high pressure and temperature within the mantle

45. Complete STSE Complete Lab 4 Part 1