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 B. Metamorphic rocks- formed when rocks that already exist are changed by heat and pressure into new kinds of rocks.
II. Rock types 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.
III. Igneous Rock Formation A.Magma - molten (liquid) rock found beneath the earth’s surface. Intrusive Rock - rock formed underground when magma cools
III. Igneous Rock Formation A.From Magma (Intrusive ) Cooled slowly Deep Shallow Large/Coarse Small Crystals Crystals
III. Igneous Rock Formation B. Lava - magma on the surface of the earth Extrusive Rock - rock formed on the surface when lava cools
III. Igneous Rock Formation B.From Lava (Extrusive) Cooled quickly Surface Fine Crystals Glassy Rocks
IV. Igneous Rock Characteristics A. Felsic (feldspar and silica--Granitic, Continental) Chemistry: High percent of silicates (Si) and water. Low percent of iron (Fe), calcuim (Ca), & magnesium (Mg) Color: Light colored minerals Viscosity: More viscous (Thick--Low temperatures and slow flowing) Trapped gases: H 2 O, O, CO 2, H 2, CO, H 2 S, SO 2 Density: Low level (high gas content)
IV. Igneous Rock Characteristics B. Mafic (Magnesium and iron--Basaltic, Oceanic) Chemistry: Low percent of silicates (Si). High in Ca, Fe, Mg. Color: Dark colored minerals Viscosity:Low viscosity (thin--high temperature and more fluid) Trapped gases: fewer present Density: Higher level (few gases)
IV. Igneous Rock Characteristics C. Andesitic (Intermediate, Continental) Chemistry: Intermediate percent of silicates (Si). Intermediate in Ca, Fe, Mg. Color: Intermediate colored minerals Viscosity: Intermediate viscosity (fluidity) Trapped gases: Intermediate amounts present Density: Intermediate level
IV. Igneous Rock Characteristics (D. Review) A.FelsicB.Mafic Mostly lightMostly dark colored minerals colored minerals [ Si] [Ca, Fe, Mg] C. Andesitic Contain light and dark minerals Intermediate levels of [Si, Ca, Fe, Mg]
IV. Igneous Rock Characteristics (D. Review) A. Felsic Dissolved B. Mafic Dissolved Gases Gases Thick & SlowThin & Fast Hard For GasesGases Escape To Escape Easily Explosive Eruptions “Gentle” Eruptions Note: Dissolved Gases Include H 2 O, S, CO 2, H 2, CO, H 2 S, SO 2
VI. How we study 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).
Small crystals Large crystals Fine crystals Felsic Andesitic Mafic
VI. How we study rocks C. Density: mass (g) ÷ volume (ml or cm 3 ). 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). =(C4/D4)