Lecture on Rocks and Rock Cycle

Overview

• Lecture covers rock types and the rock cycle.
• Mention of field trips and specialized classes on geology and related subjects at Santa Barbara City College.

Quotes and Philosophical Notes

• Reference to Ralph Waldo Emerson's quote: "A foolish consistency is the hobgoblin of little minds."
• Discussion on the idea of consistency and its implications.

Rock Cycle

• Earth is constantly recycling itself: carbon cycle, hydrologic cycle, chemical cycles, cycle of life.
• Rock cycle involves old rock being pushed into the earth and new rock being formed.
• Examples of old rock: Canadian Shield, Appalachian Mountains.

Types of Rocks

1. Igneous Rocks

   • Formed from magma that comes from inside the earth.
   • Example: Obsidian (volcanic glass).
   • Can be classified as intrusive or extrusive.

2. Sedimentary Rocks

   • Formed from the compression of small, broken-down pieces of other rocks.
   • Often found with fossils due to their softer nature.
   • Example: Limestone (often forms underwater).
   • Types: Clastic (rock and mineral fragments), Chemically Precipitated, Organic.

3. Metamorphic Rocks

   • Formed from sedimentary rocks that have been heated and pressurized.
   • Example: Gneiss (from granite), Marble (from limestone).

Minerals

• Building blocks of rocks: chemical crystalline compounds.
• Examples: Gold, Pyrite, Graphite.
• Minerals have specific shapes based on their chemical bonds (e.g., hexagonal, cubic).
• Example minerals shown: Sodalite, Quartz.

Identification of Rocks and Minerals

• Identification methods: shape, color, sheen, and sometimes taste.
• Color can indicate mineral content: felsic (light-colored), mafic (dark-colored), ultramafic (very heavy and dark-colored).
• Example: Yosemite's Half Dome (a batholith, a large intrusive igneous rock formation).

Specialized Rock Formations

• Batholith: A large collection of plutons, forms deep in the Earth's surface.
  • Example: Sierra Nevada mountains.
• Dike: An intrusive formation that cuts across strata.
• Sill: Intrusive magma wedged between layers of strata.
• Laccolith: Magma that creates a lump between layers of strata.
• Xenolith: A rock surrounded by newer intrusive rock.

Additional Notes

• Different processes result in various rock formations, including mountain building (orogeny).
• Lecture mentions several videos that provide additional visual examples of the rock cycle and rock types.
• Next lecture topics: volcanoes and earthquakes.