Notes Unit 1:

 

 

MINERALS

 

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Minerals are made from elements. Elements are substances that cannot be broken down by normal chemical means. All elements are listed in the Periodic Table of Elements. Some common elements in minerals are Oxygen (O), Silicon (Si), Calcium (Ca) and Sodium (Na).

NOVA Video on Minerals

Brief Introduction to Minerals

 

All minerals have four properties:

1. All minerals are naturally occurring

2. All minerals are inorganic (that means non-living)

3. A different chemical formula can be written for each mineral and that formula is constant for that mineral.

ex. Galena is PbS- it has one lead atom (Pb) and one sulfur (S) atom in each molecule.

4. Most minerals have an unique crystalline shape given the right growing conditions (as in a cave).

 

Identifying Minerals

 

Minerals have many different properties, and geologists use these properties to determine what kind of mineral is before them. Scientists use a combination of properties to distinguish between these minerals, using the process of elimination.

Video on Identifying Minerals

The following is a description of each of these properties:

1. Color-

Color is usually the first property observed when handling a specimen. Color alone is not reliable, but it can help us to eliminate possibilities. We must be sure we have a freshly exposed surface, because weathering can change the color of a mineral. Some minerals, such as sulfur, always have the same color (yellow). Other minerals may have different colors. One example is quartz, which may be clear, purple, pink and even gray!

 

2. Luster-

Luster is the way light reflects from a mineral's surface. Luster is either metallic or nonmetallic. Metallic minerals look like.... well, a metal. Nonmetallic minerals can be glassy, dull, brilliant, waxy, earthy, or pearly.

 

3. Streak-

The color of the powder of a mineral when scraped on a porcelain plate. Oddly sometimes the powder of a mineral can be different from color of the mineral itself. Pyrite (fool's gold) is gold in color, but its streak color is dark gray or black! Weird, huh?

 

4. Hardness-

Hardness is a mineral' s ability to resist being scratched. Talc, the softest mineral, can easily be scratched with a finger nail. Diamond is so hard that it can't be scratched by another mineral. Hardness does not describe a substance's ability to resist being broken. Even though diamond is the hardest mineral, it can be broken if you smash it with a hammer. To show the hardness of mineral, we use:

Moh's Scale of Hardness.


Talc- 1 Softest
Gypsum- 2
Calcite- 3
Fluorite- 4
Apatite- 5
Orthoclase- 6
Quartz- 7
Topaz- 8
Corundum- 9
Diamond- 10 Hardest

To determine the hardness of a mineral, scratch it with these minerals, and find out which minerals will and won't scratch it, and you know that mineral's hardness falls between those minerals. For instance, if a mineral is not scratched by Quartz, but is scratched by Topaz, the hardness must be between 7 and 8. Get it?

 

4. Cleavage-

Cleavage is the tendency of a mineral to break parallel to atomic planes in its crystalline structure. Perhaps the best example of cleavage is Muscovite mica, which is a mineral that breaks in parallel sheets. Mica always flakes off in thin sheets, like pieces of paper off of a giant stack of papers. Its atoms line up in sheets, and this is what provides a plane of weakness. Another example is Halite, that has cleavage in three directions at angles of 90 degrees from each other. When a piece of Halite is broken, it breaks into many smaller cubes.

Fracture is when a mineral breaks into jagged edges. Some minerals have no planes of weakness, so they have no cleavage.

Some minerals have a distinct fracture. Quartz is a perfect example. Obsidian always fractures in a pattern that looks like a clam shell. Obsidian is also called volcanic glass.

 

5. Crystals-

Crystal Shape is the natural geometric shape of a mineral. Minerals grow into different shapes because the internal arrangment of their atoms form unique patterns. Each layer is built up much like layers of chocolate would on an ice cream cone dipped again and again into melted chocolate sauce. Minerals must have time to grow slowly.

ex. Quartz crystals form hexagonal shapes, salt, diamonds and pyrite are cubic, and mica is monoclinic.

 

5. Other Properties-

Some minerals have special properties.

Magnetic minerals, such as magnetite, give a magnetic tug when close to magnets. In fact, early compasses where made by floating magnetite on a piece of wood in water.

Fluorescent minerals glow under UV (black) light. Some of the colors are amazing! ex. Calcite

Radioactivity- some minerals emit radiation such as uraninite which contains uranium.

Double refraction is a dead give away property of Iceland spar calcite. When this mineral is placed on paper you see double!

Reaction to Acid- HCl, or hydrochloric acid, can be used to identify calcite or limestone. Calcium Carbonate bubbles furiously when acid is applied.

Halite (NaCl) is tested by using your sense of taste. If you lick it, it tastes very salty, because salt is actually made from Halite.

 

Minerals are the building blocks of rocks. Nearly one hundred of the thousands of known minerals make up ninety five percent of the earth's rocks. Twenty of these minerals are most likely to be found in rocks found in the field.

 

 

ROCKS

 

Rock Cycle

The rock cycle is the constant changing of rocks from one form to another. Any rock type can form from any other rock type.

Rock Cycle Reference Table video

Bill Nye on Rocks video

Untamed Science on Rock types video

Igneous Rocks

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Igneous rocks form by the crystallization of lava, molten rock cooling on the surface of the earth or magma, molten material solidifing inside the earth.

Extrusive Volcanic Rock

Formed when molten (liquid) rock called lava hardens quickly on the Earth's surface.

Biggest Volcanic Eruptions video

Really fast cooling lava does not give crystals time to grow and form. So the rock formed has a glassy texture.

ex. Obsidian

If the lava cooled a little more slowly, crystals will form but they are still invisble to the eye. You would need a magnifying glass to see them.

ex. Basalt

If the lava had air pockets in it it would harden with a bubbly texture called Vesicular Texture.

ex. Scoria and Pahoehoe

Intrusive Plutonic Rock

Formed when molten rock hardens slowly deep inside the earth.

The more time a crystal has to form, the larger the crystal will be.

If given a long enough time to cool, crystals can get really big! Magma that is stuck underground will cool very slowly, because it is insulated by the surrounding rock. So for hundreds of years, crystals can grow to 12 meters and more. Some magma chambers cool only a few degrees per century.

Mexico's Giant Crystal video

The intrusive igneous rocks you'll see in class will be around 1 inch sized crystals that interlock together like puzzle pieces.

ex. Granite and Gabbro

Igneous rocks are identified based on their texture and mineral composition.

Texture is the size of mineral crystals.

Mineral composition is simply the minerals that make up an igneous rock.

Felsic or light colored igneous rocks, like granite, are listed in your reference table as having lots of quartz and feldspar in it. Mafic or dark rocks like basalt is heavy in density and made of proxene and amphibole (hornblende).

Igneous Rocks and the Reference Tables video

 

 

Sedimentary Rocks

Sediments (broken bits of rock) are formed by the weathering of rocks by wind, water, or ice. Most sediments are rock, but some can be pieces of plants or animals. When these materials are deposited, they form loose layers which then gets cemented into solid rock layers.

Bill Nye on Sedimentary Rocks

Photos of Sedimentary Rocks

 

Types of Sedimentary Rock

Clastic- Made of sediments held together by compaction and cementation (rock glue).

In order of increasing size, common clastic rocks include Shale, Siltstone, Sandstone and Conglomerate (or Breccia).

The more rounded the sediments making up the rock, the more it has tumbled in a stream.

Chemical or Crystalline- Forms when mineral grains precipitate out of solution by water evaporating.

Ex. Rock Salt or Gypsom

Organic or Bioclastic- Animal or plant remains make up compacted and altered rock.

Coal is made of squashed plants and Fossil Limestone is formed when animal skeletons sink to the bottom of the sea and collect. In New York they found two mastodon skeletons in 2000!

Sedimentary Rock Video

Sedimentary GeoScience Video

 

Classification of Sedimentary Rocks

Most sedimentary rocks are formed by deposition of sediment in shallow seas, oceans and lakes. They are laid down in flat layers (a great identifying feature) and sometimes contain fossils.

The clastic sedimentary rocks are classified by grain size.

Sedimentary Rocks and the Reference Tables

Identifying Sedimentary Rocks

 

 

 

Metamorphic Rocks-

Metamorphic rocks are formed by changing sedimentary, igneous or metamorphic rock. Heat and pressure can cause the formation of metamorphic rocks through contact with magma and/or deep burial.

Heat-

Most minerals expand when heated, causing atoms to move apart, stretching the bonds that hold them together. If heated enough, the bonds will break, and the mineral melts. In a metamorphic rock, some bonds break, but not all, so some changes take place but the rock does NOT melt. Metamorphic rocks have a different set of characteristics than its original form. One example is limestone. When it is "baked" by the contact with magma, it turns into marble.

Pressure-

Pressure has the opposite effect of heat. It pushes the atoms within rocks together. This pressure will result in some sort of deformation. Often, rocks seem to have bands that are twisted and turned, resulting from metamorphosis of sedimentary rocks.

Good ways to identify a metamorphic rock include layers of flattened crystals, distorted structure and the appearance of exotic crystals.

Metamorphic Rocks and the Reference Table

Metamorphic Rock Video

 

 

Characteristics of Metamorphic Rocks

 

Change to Crystalline Texture-

During metamorphosis, the size, spacing, and shape of the grains are changed. They may fuse due to heating and create brand new, large crystals. In New Hampshire they found a single crystal of Beryl had grown to be 250 feet long! Garnet schist is a good example of a rock that grew bizarre crystals with help from metamorphosis.

Increased Density-

Pressure which forces the grains closer together can cause the volume to decrease, while the mass remains the same. The density of the rock increases.

Foliation and Banding-

Sometimes, heat and pressure can produce a thin layer of flattened crystals aligned on the same plane called foliation. Foliation can be extreme when minerals recrystallize and separate out according to density, like oil and water. For example gneiss has has wavy stripes of black and white crystals. Extreme foliation is called banding.

Distortion of Layers-

When a sedimentary rock is metamorphosed, its layers become distorted (that means the layers are wavy).

 

Review:

Rock Cycle Rap- Mr. Lee

The Rock Cycle Rap- Mr. Beasley

The Rock Cycle Song