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Geology of the Pacific Northwest

Geology-208

Week 2:  READING THE ROCKS OF WASHINGTON

Minerals

Mineral Characteristics

Minerals—the building blocks of rocks—are formed from elemental compounds made up of atoms, the building blocks of the universe. The following characteristics are true of minerals. They are:

Mineral Examples

Table salt, ice, snowflakes, and shells are mineral because they fit all of the criteria. Table salt is made up of alternating sodium and chloride atoms (NaCl, also known as halite). Snowflakes have 6 crystal points. Shells are made of calcite—a combination of calcium, carbon, and oxygen in the form of CaCO3 .

Non-Mineral Example

Glass is a chilled, thick, viscous liquid that runs too slowly to be seen by the human eye. Glass is not solid and cannot be classified as mineral.

Mineral Families

  1. Native Elements (gold, silver, copper, platinum, diamond)
  2. Silicates (75% of the Earth's crust: felsic, high in silica, and mafic, low in silica.) [The "-ates" ending means the mineral group includes oxygen.]
  3. Carbonates (carbon and oxygen). Their carbon content causes them to bubble when hydrochloric acid is applied.
  4. Sulfates (sulfur, oxygen)
  5. Oxides (oxygen; i.e., iron oxide: magnetite)
  6. Sulfides (sulfur)

Mineral Formation

Every mineral is found in a certain environment (pressure, depth). A rock's shape is determined by the structure of its atoms. Its color is determined by its mineral makeup.

Rocks

Rock Forms

Three main forms of rock found in the Northwest are: igneous rocks (formed from cooled, crystallized molten rock), sedimentary rocks (formed from compacted, lithified fragments), and metamorphic rocks (changed mineralogically by increased temperature and pressure).

Rock Cycle

The life of a rock begins and ends as magma. Cooled by contact with the atmosphere or water, magma solidifies into igneous rocks like granite, obsidian, or pumice. Weathered igneous rocks erode and become sediment which is transported by glaciers, rivers, and winds and deposited in other places. Compacted sedimentary deposit is lithified into sedimentary rock such as coal, limestone, or sandstone. Sedimentary rock that is subjected to high pressures and temperatures becomes metamorphic rock like marble or slate. If rock temperatures and pressures increase, metamorphic rocks melt and return to magma.

Rock Properties

To identify a rock or mineral, gather information about its physical properties:

Tools

RESOURCES

The Rock Cycle (University of British Columbia; 4 January 2000)
Introduction to Minerals (Gore, Pamela J.W.; July 17, 1999)
• Pellant, Chris, 1992, Rocks and Minerals (Dorling Kindersley, London, pp.256)

GLOSSARY



Send comments to Rob Viens (e-mail: rviens@bcc.ctc.edu) or call him at his Bellevue Community College office at (425) 564-3158. Office hours are by appointment.


© 2001-2002, Rob Viens, Bellevue Community College. All rights reserved.
Page updated on 5 September 2002  • 
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