Geoscience Education Lessons
EDUCATION COMMITTEE
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Rocks and Minerals
INSTRUCTOR
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Rocks vs Minerals
Rocks are the foundation of the earth and are composed of one or more minerals.
Rock
A naturally occurring solid substance composed of one or more minerals.
Mineral
A naturally occurring, inorganic compound having an orderly internal structure and chemical composition, crystal form, and physical properties.
Rock Cycle
Rocks are classified into three categories according to how they are formed:
Magma
Sediments
Heat and Pressure
Where do rocks come from?
The rock cycle helps us understand what conditions helped formed those rocks, which can tell us a lot about the history of a region.
Where do rocks come from?
The geosphere, hydrosphere, atmosphere, and biosphere all play a role in the formation of rocks.
Explore the Rock Cycle
Let's check out some rocks!
Igneous Rocks
Extrusive (Volcanic)
Igneous Rocks
Igneous Rocks Texture
Texture: Glassy
Igneous rock with no mineral grains.
Magma cools rapidly that minerals do not have a chance to crystalize.
Example: Obsidian
Texture: Vesicular
Igneous rock with no mineral grains.
Very fast cooling, rapid gas escape forming bubbles.
Example: Vesicular Basalt
Texture: Aphanitic
Igneous rock composed of crystals that are too small to see with the naked eye.
Fast cooling
Example: Basalt
Texture: Phaneritic
Igneous rock composed crystals that are large enough to be seen with the naked eye or hands lens
Slow cooling
Example: Granite
Texture: Porphyritic
Igneous rock composed of magma that cooled slowly at first, then more rapidly as the magma neared the surface
Large crystals together with smaller crystals
Example: Rhyolite
Mineral Properties
Minerals can be identified by their physical properties
Mineral Properties: Hardness
A German mineralogist named Friedrich Mohs (1773-1839) set up a testing scale in 1822 for measuring the hardness (H) of minerals. He discovered that materials such as glass, fingernails, knives, nails, other minerals, etc. could be used to test the hardness of a mineral in question.
Mineral Properties: Hardness
Testing Hardness
Mohs Hardness Scale
1 = softest
10 = hardest
If the mineral scratches, the mineral is softer than the object
Mineral Properties: Streak
What color is the mineral powdered.
Streak on a ceramic tile.
Mineral Properties: Luster
How light is reflected
Mineral Properties: Cleavage/Fracture
Cleavage
Planes of weakness, when a mineral breaks into a flat surface
How does the mineral break?
Fracture
Mineral breaks along curved surfaces without a definite shape
Do not have planes of weakness
Importance of Minerals
Human Health
Industrial Applications
Examples of Minerals
Copper
(ex: automobiles, planes)
(ex: plumbing, HVAC)
Examples of Minerals
Lithium
Examples of Minerals
Magnesium
(ex. smartphones, laptops, car seats)
(ex. steel & iron)
Examples of Minerals
Barite
Examples of Minerals
Gypsum
Examples of Minerals
Gold
Metamorphic Rocks
Rocks that form from other pre-existing rocks, that have been changed from high temperatures and/or high pressure
All changes occur in the solid state, without passing through a liquid form.
Metamorphic Parent Rock
The original rock from which a given metamorphic rock is formed.
Can be any rock type: igneous, sedimentary, or metamorphic
Sedimentary Rock
Composed of small mineral and rock fragments produced by weathering.
Sediment can be deposited on the land, ocean, or body of water, which is then compacted and cemented into a rock known as lithification.
Sedimentary Rock
Compaction: packing sediment together through burial
Cementation: minerals precipitate from sediment pore fluids to bind sediment, calcite and quartz common cements.
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Weathering
Weathering processes break rock into pieces, sediment.
These fragments are transported via gravity, wind, water or ice, to a new location where they are deposited.
Sediment is lithified to form sedimentary rocks.
Chemical Sedimentary Rocks
Directly precipitate out of water, that becomes compacted and cemented together
Precipitation occurs when water becomes supersaturated with dissolved minerals
Examples: Rock salt, gypsum, limestones
Sedimentary Rocks Clastic
Formed when solid fragments of pre-existing rocks are deposited and then lithified.
Classified by:
Chemical Sedimentary Rocks
Biochemical Sedimentary Rocks
Form due to a chemical change that involves a living organism.
Processes that involve living organisms which produce the sediment.
Classified primarily by chemical makeup.
Most limestones and coals are produced by this process.
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