1. Rock Types
IGNEOUS ROCKS( )

2. Igneous Rocks form underground or near the surface, from the crystallization of magma.
Magma – molten rock underground
Lava – magma reaches Earth’s surface

3. What is Porphyritic Texture?
Porphyry – Where large crystals are surrounded by the rest of the rock. Usually represents 2 or more stages of eruption or cooling. “CRYSTAL CHUNKS”

4. HIGH PORPHYRY tells you. .
The rock cooled underground
The rock took a long time to cool
The rock could have melted and cooled several different times

5. Igneous rocks are very strong because of interlocking crystal grains. . .
When there is not enough “room” for crystals to grow large, they fuse with each other.

6. “Vesicular” texture means having bubbles. . .
These normally depend on the thickness of the lava, and whether gases can get trapped.

7. There are two types of Igneous Rock, based on the elements/ minerals they’re made of . . .
MAFIC -- “DARK” . Rich in Iron and Magnesium. Are dark colored, grainy textured, with low luster. Low porphyry.
FELSIC – “LIGHT” . Rich in Silica (glass) . Contain colors such as tan, pink, cream, light grey, etc. High luster, or large crystals present. Greater porphyry.

8. MAFIC FELSIC

9. The other classification we use, is the location where rocks cooled off.
Intrusive – Cooled slowly beneath earth’s surface. These will contain a variety of crystals, because they had a longer time to form.
Extrusive -- Cooled quickly at or just below the surface. Very little / no porphyry.

10. INTRUSIONS -- A long “tube” of igneous rock that came in through a vent/crack underground , and cuts across older rock. (Also known as veins / dikes – “INTRUDER”)
Pegmatites: Felsic veins with very large, chunky crystals.
Kimberlites: Mafic veins. (DIAMONDS are found in these)

11. Local Evidence of Extrusive Igneous Rocks
“Lava Caps” down Latrobe Road,
And Scoria in the fireplaces
In older homes in EDH!

12. Local Evidence of Intrusive Igneous Rocks
Sierra Nevada Granite formations up highway 50 and

13. When we learn about rock types this time, we will classify them in this manner . . .
IGNEOUS ROCK Intrusive Extrusive Mafic Felsic Mafic Felsic

14. EXTRUSIVE MAFIC
SCORIA: Large bubbles, concrete-like texture, brittle, dark in color. From thick, pasty lava. BASALT: Dark, grainy, dense rock. Comprises the crust of the ocean floor

15. INTRUSIVE MAFIC
GABBRO: Dark background with large, dark crystals present.

16. EXTRUSIVE FELSIC
PUMICE: Can float, very Small bubbles (vesicular), from thin lava. Texture of spun glass. RHYOLITE: Salmon to cream color, may have very small splinter- Like crystals. OBSIDIAN: Volcanic glass ANDESITE :Light color, low porphyry

17. INTRUSIVE FELSIC
DIORITE (Granite): High porphyry. What most of the Sierra Nevadas are made of!