Igneous Rocks Chap. 5 What are igneous rocks? Identifying igneous rocks.
Rocks
description
Transcript of Rocks
http://www.beg.utexas.edu/mainweb/publications/graphics/granite.htm
http://en.wikipedia.org/wiki/File:USDA_Mineral_Sandstone_93c3955.jpg
http://www.gccaz.edu/earthsci/imagearchive/gneiss.htm
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:
SEDIMENTARYIGNEOUSMETAMORPHIC
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.
A mineral isNaturally occurringInorganicDefinite chemical composition & crystalline
structureSolid
All physical properties of minerals come from the “internal arrangement of atoms”
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 shinethe only way to really learn the different
lusters is to see them for yourself.
Metallic- looks like shiny metalNon-metallic- all the other ways that a mineral
can shineGlassy/vitreous- shines like a piece of broken glass
(most common non-metallic)Dull/earthy- no shine at allResinous/waxy- looks like a piece of plastic or dried
gluePearly- 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
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.
1. Talc (Softest)2. Gypsum3. Calcite4. Fluorite5. Apatite6. Feldspar (AKA Albite)7. Quartz8. Topaz9. Corundum10. Diamond (Hardest)
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
Cleavage -To break along flat surfaces.Examples of CleavageCubic- To break into cubesRhombihedral- to break into “pushed over
cubes” Basal- to split into thin sheets
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
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.
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.
Light-colored, coarse- grained, no pattern
Mostly quartz, feldspar, mica, and hornblende
Often used for buildings and monuments
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
Dark-colored, coarse- grained intrusive
Similar composition to basalt—plagioclase feldspar with some pyroxene and olivine
Natural volcanic glassForms when lava
cools very quicklyUsually dark, but
small pieces may be clear
Fractures along curved (conchoidal) surface
Used as spear and arrow points, knives
Light colored, frothy (many air spaces)
Same minerals as in granite, but finer in grain size
Sedimentary rocks may be made of rock fragments—sediments—or by chemical reactions. The classification of sediments is shown below.
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.
Shale is the most common sedimentary rock
Sedimentary rocks cover about three-quarters of the land surface
For more about sedimentary 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
Gneisses and schists are common in New York City and Westchester.
http://www.state.nj.us/dep/njgs/
One of the most abundant minerals in the world (Quartz and feldspar fight for #1)
Makes beach sandMakes glass (melted beach sand)- Sweet Home
AlabamaChemical formula: SiO2Since 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 = 4hedron =“sided solid
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.htmBibliographyDr. Michael J. Passow
http://www.mrsciguy.com/rocks.html