ROCK NOTES. I. What is a rock?. Rock - two or more minerals (found in the earth’s crust) bound together in a solid form. II. Rock types. A. Sedimentary rocks - formed by the hardening and cementing of layers of sediment. II. Rock types.
Rock - two or more minerals (found in the earth’s crust) bound together in a solid form
A. Sedimentary rocks- formed by the hardening and cementing of layers of sediment.
B. Metamorphic rocks- formed when rocks that already exist are changed by heat and pressure into new kinds of rocks.
C. Igneous rocks- formed by cooling and hardening of hot molten rock from inside the Earth. Hot molten rock from inside the earth is called magma.
A. Magma - molten (liquid) rock found beneath the earth’s surface.Intrusive Rock - rock formed underground when magma cools
A. From Magma (Intrusive )
B. Lava - magma on the surface of the earthExtrusive Rock - rock formed on the surface when lava cools
B.From Lava (Extrusive)
A. Felsic (feldspar and silica--Granitic, Continental)
B. Mafic (Magnesium and iron--Basaltic, Oceanic)
C. Andesitic (Intermediate, Continental)
A. Felsic B. Mafic
Mostly light Mostly dark
colored minerals colored minerals
[ Si] [Ca, Fe, Mg] [ Si] [Ca, Fe, Mg]
Contain light and dark minerals
Intermediate levels of [Si, Ca, Fe, Mg]
A. Felsic Dissolved B. Mafic DissolvedGases Gases
Thick & Slow Thin & Fast
Hard For Gases Gases Escape
To Escape Easily
Explosive Eruptions “Gentle” Eruptions
Note: Dissolved Gases Include H2O, S, CO2, H2, CO, H2S, SO2
Darker colored rocks
Lighter colored rocks
A. Color: Lightness/darkness indicates chemistry. Darker rocks tend to have more iron (Mafic),lighter rocks have more silicon (Felsic).
B. Crystal size: Can be measured in millimeters using a hand lens/microscope and ruler. Larger crystals need more time to form and are found in rocks that cool slowly (intrusive).
C. Density: mass (g) ÷ volume (ml or cm3).
More dense rocks formed from magma that originates deeper in mantle (less explosive volcanoes) and contain fewer gases (Mafic).
Less dense rocks formed from magma that originates from outer mantle (more explosive volcanoes) and contain more trapped gases due to interaction with ocean water (Felsic).