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Rocks

Rocks. http://en.wikipedia.org/wiki/File:USDA_Mineral_Sandstone_93c3955.jpg. http://www.beg.utexas.edu/mainweb/publications/graphics/granite.htm. http://www.gccaz.edu/earthsci/imagearchive/gneiss.htm. This slide show is intended to help you understand important types of rocks.

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Rocks

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  1. Rocks http://en.wikipedia.org/wiki/File:USDA_Mineral_Sandstone_93c3955.jpg http://www.beg.utexas.edu/mainweb/publications/graphics/granite.htm http://www.gccaz.edu/earthsci/imagearchive/gneiss.htm

  2. This slide show is intended to help you understand important types of rocks. The diagram in the next slide represents the ROCK CYCLE—a scheme that represents the processes of continuous changes that connect the three major groups of rocks: SEDIMENTARY IGNEOUS METAMORPHIC It also shows two other important parts of the “Rock Cycle” – SEDIMENTS and molten LAVA and MAGMA Note about image sources: Many images come from a website (Volcano World) that no longer is supported, so no credit is given. The last slide provides possible sources.

  3. Here is another version of the Rock Cycle

  4. Mineral Identification • A mineral is • Naturally occurring • Inorganic • Definite chemical composition & crystalline structure • Solid • All physical properties of minerals come from the “internal arrangement of atoms”

  5. The Color Test- easiest test to do but not always reliable • The Streak Test -The color of the powdered mineral. • Performed by rubbing the unknown mineral on an unglazed tile. • The Luster Test -the way a mineral shines or doesn't shine • the only way to really learn the different lusters is to see them for yourself.

  6. Types of Luster • Metallic- looks like shiny metal • Non-metallic- all the other ways that a mineral can shine • Glassy/vitreous- shines like a piece of broken glass (most common non-metallic) • Dull/earthy- no shine at all • Resinous/waxy- looks like a piece of plastic or dried glue • Pearly- looks oily it may have a slight rainbow like an oil slick on water. Also looks like the inside of some clam shells • Adamantine- brilliant, sparkling shine like a diamond

  7. Hardness • Hardness- a minerals resistance to scratching. This should not be confused with brittleness. A diamond is very hard and will scratch a hammer but a hammer will smash a diamond. Likewise, talc, one of the softest minerals, is not squishy. It will still put a serious hurting on you if you get hit in the head with it.

  8. Moh’s Scale of Hardness • 1. Talc (Softest) • 2. Gypsum • 3. Calcite • 4. Fluorite • 5. Apatite • 6. Feldspar (AKA Albite) • 7. Quartz • 8. Topaz • 9. Corundum • 10. Diamond (Hardest)

  9. Key Points of a Hardness Test • Choose one mineral to be the scratcher and one to be the scratchee. • Pick a smooth, flat surface to scratch. • After doing the test, wipe the powder away to confirm that the scratchee really got scratched. • If the scratchee did not get scratched, switch the two rocks and repeat. • Hardness Tools • Fingernail 2.5 • Penny 3.5 • Iron Nail 4.5 • Glass Plate 5.5 • Steel File 6.5 • Streak Plate 7

  10. Cleavage • Cleavage -To break along flat surfaces. • Examples of Cleavage • Cubic- To break into cubes • Rhombihedral- to break into “pushed over cubes” • Basal- to split into thin sheets

  11. Fracture • The way a mineral without cleavage breaks. • Examples of Fracture • conchoidal- to break in a scooped out bowl shape- like a conch (sea snail) • hackly fracture- to have irregular sharp edges • splintery- to break into long, thin needles

  12. Miscellaneous Tests • Acid- Calcite and powdered dolomite will effervesce (fizz) in dilute hydrochloric acid (HCl) • Smell- Sphalerite will give off a rotten-egg smell when streaked on a streak plate. (Note: pure sulfur does not smell like rotten eggs!) • Magnetism- Magnetite (AKA Lodestone) will pick up paper clips (weak samples will only be able to pick up staples) • Taste- Halite is rock salt and will taste salty. *Do not taste the samples since some have been tested with acid to see if it is calcite. • Fluorescence- some minerals (mostly forms of calcite) will glow in fluorescent colors under a black (UV) light.

  13. IGNEOUS ROCKS • Form by solidification (crystallization) of melted minerals • At the surface, LAVA hardens to form EXTRUSIVE rocks with tiny (FINE-GRAINED) crystals or GLASSY (no crystal) TEXTURES • Beneath the surface, MAGMA hardens to form INTRUSIVE rocks with easily visible (COARSE-GRAINED) crystal texture.

  14. Granite • Light-colored, coarse- grained, no pattern • Mostly quartz, feldspar, mica, and hornblende • Often used for buildings and monuments

  15. Basalt • Dark-colored, fine- grained, extrusive • Formed where lava erupted onto surface • Most widespread igneous rocks • Found locally in the Palisades along west shore of Hudson River, Connecticut River valley

  16. Gabbro • Dark-colored, coarse- grained intrusive • Similar composition to basalt—plagioclase feldspar with some pyroxene and olivine

  17. Obsidian • Natural volcanic glass • Forms when lava cools very quickly • Usually dark, but small pieces may be clear • Fractures along curved (conchoidal) surface • Used as spear and arrow points, knives

  18. Pumice and other igneous rocks • Light colored, frothy (many air spaces) • Same minerals as in granite, but finer in grain size

  19. Sedimentary Rocks Sedimentary rocks may be made of rock fragments—sediments—or by chemical reactions. The classification of sediments is shown below.

  20. Clastic rocks–made of cemented sediments—are classified by their grain sizes.

  21. Non-clastic rocks form by chemical precipitation (settling out from a solution.) Limestone is made from calcite, chert from quartz, and halite is rock salt.

  22. Biologic sedimentary rocks come from the remains of organic matter. • The most important of these is coal. Anthracite coal results from the greatest pressure and releases the most energy when burned. Other varieties are bituminous and lignite. “Petrified” (permineralized) wood is another organic rock.

  23. More about sedimentary rocks • Shale is the most common sedimentary rock • Sedimentary rocks cover about three-quarters of the land surface • For more about sedimentary rocks:

  24. Metamorphic Rocks • Formed by heat and pressure changing existing rocks • REGIONAL METAMORPHIC affects a large area and results from plate tectonics • CONTACT METAMORPHISM affects rocks on a local scale, such as “baking” sedimentary rocks next to magma or lava

  25. “Foliated” rocks contain much mica and other rocks that produce layering or banding Gneisses and schists are common in New York City and Westchester.

  26. Non-foliated metamorphic rocks include marble, which comes from limestone, and quatzite, which comes from sandstone

  27. Locations, types, and ages of the bedrocks are represented in a geologic map http://www.state.nj.us/dep/njgs/

  28. A little about Quartz: • One of the most abundant minerals in the world (Quartz and feldspar fight for #1) • Makes beach sand • Makes glass (melted beach sand)- Sweet Home Alabama • Chemical formula: SiO2 • Since it is SiO2, there is twice as much oxygen as silicon. • Oxygen is the #1 element in the crust with Silicon #2 (and about half that of Oxygen) • Crystal shape is a pyramid called a “tetrahedron” • Tetra = 4 • hedron =“sided solid

  29. Additional Resources There are many web sites that can provide you with more information about rocks and images. Here are a few: http://www.gccaz.edu/earthsci/imagearchive/gneiss.htm http://geology.about.com/library/bl/images/blrockindex.htm Bibliography Dr. Michael J. Passow http://www.mrsciguy.com/rocks.html

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