MINERALS
What are they?
- Solid
- Naturally occurring
- Inorganic elements or compounds
- Has a specific composition
- Has a definite crystalline structure
What is a crystal?
- Solid
- Made of atoms
- Atoms organized in repeating patterns
How are they formed?
- Formed from hot liquid rock called magma or
- Supersaturated solutions
What is meant by supersaturated solution?
- When individual atoms can bond (join) together, and mineral crystals precipitate or settle to the bottom of a container; this precipitate form into solid from a solution.
How do we identify minerals?
- Scientists use the physical and chemical properties of minerals through the several combinations of tests to identify them.
- Examples of properties include:
- luster
- hardness
- cleavage or fracture
- streak
- double refraction
- effervescence
- fluorescence
- magnetism
- striations
- color
- crystal formation
Note that color and crystal formation are the least useful in identifying minerals.
How are minerals classified?
- Based upon their chemical properties and characteristics and placed into groups that include:
Silicates (Si, O, and other elements)
Carbonates (metallic elements and CO3)
Oxides (O and a metal)
Sulfides (S and other elements)
Sulfates (SO4⁻² and other elements)
Halides (Cl or F along with Ca, Na, or K)
Native elements (Ag or Cu)
What are some of the benefits of Minerals?
- We use them in many products such as computers, cars, TV’s, desks, roads, buildings, beds, medicine, jewelry, medicine, etc.
How can minerals be obtained?
- Minerals are found in ores, rocks containing valuable substances such as gold or silver.
- Examples of ores include hematite that contains iron for bridges or bauxite that contains aluminum for windows or ilmenite that contains titanium for wheelchairs.
What are other economic benefits of minerals?
- Some valuable minerals are considered gems as they are used for jewelry.
- Gems are valuable for their rarity and beauty such as diamonds, rubies, and emeralds.
- Gems are very hard substances, and they are scratch-resistant (can’t be scratched easily).
Note that the purer the gem, the more expensive it is!
***For example, a diamond is formed from carbon and it has other impurities. The less impurity a diamond contains, the more expensive it is.***
Minerals: Igneous Rocks
What are igneous rocks?
- They are rocks that have formed directly from the hot liquid rock inside earth called magma as it has cooled and crystalized over time.
What is magma made up of?
- Molten rock
- Dissolved gases
- Mineral crystals
How is magma classified?
- It depends on the content of silica present in it such as it can be:
Basaltic such as the Hawaiian Islands.
Andesitic such as Cascade Mts. & Andes Mts.
Rhyolitic such as Yellowstone National Park.
How is magma formed?
- By melting of crust or melting with the mantle.
What factors determine its formation?
- Temperature
- Pressure
- Water content
- Mineral content
How do different igneous rocks form?
- It happens through the partial melting process, that is, whenever a group of minerals melts, different elements are added to the mixture of magma, changing its composition.
How does partial melting play a role in fractional (partial) crystallization?
- Fractional crystallization is simply the reverse of partial melting: The first crystals to melt in partial melting will be the first minerals to crystallize out when the magma begins to cool, resulting in a high concentration of silica, aluminum, and potassium.
What is the relationship between the cooling of magma and the formation of minerals that form igneous rocks?
- Bowen, a scientist, discovered two ways of crystallization:
1) A continuous, gradual change of mineral compositions in the feldspar group
2) A sudden change of mineral type in the Fe-Mg groups due to decreased temperature
How do we classify igneous rocks?
- Mineral composition
- Crystal size
- Texture
What are the two types of rocks?
- Intrusive rocks
- Extrusive rocks
What are the classes of igneous rocks in terms of their mineral composition?
- Basaltic rocks
- Granitic rocks
- Intermediate rocks
- Ultrabasic rocks
How does texture play a role in crystal size formation?
- The size, shape, and distributions of crystals or grains can be either fine, glassy, or vesicular (extrusive rock).
- The size, shape, and distributions of crystals or grains can be coarse or porphyritic (intrusive rock).
What are some resources of igneous rocks?
- They are used in construction (due to being strong, durable, i.e, weather-resistant such as granite used for bridges and countertops), energy production, and jewelry making process.
What are some locations of igneous rocks?
- Veins: A long, regularly shaped occurrence of an ore, which has a limited volume within a rock and filled with crystals of minerals precipitated from an aqueous fluid.
Examples include pegmatite (rock source for Mt. Rushmore) and kimberlite (a high temperature and pressure rock source for diamonds).
Minerals: Sedimentary Rocks
How are sedimentary rocks formed?
- They are formed from pieces of rocks called sediments by the processes known as weathering and erosion.
What are weathering and erosion?
- Weathering is the process of breaking up the rocks or material into fragments called sediments.
- Erosion is the process of carrying this material from one place to another.
What are the agents of erosion?
- Wind
- Moving water
- Gravity
- Glaciers (large masses of ice sheets that move across the land)
What happens when erosion is complete?
- Deposition take place whereby the carried sediments are dropped off or left behind based on its size, heavier particles are left behind first and so on.
What happens after particle or sediment deposition?
- As more and more sediments are deposited upon each other, the increasing pressure and temperature solidify these sediments through the lithification process.
What is lithification?
- It is the physical and chemical processes that change sediments into sedimentary rocks through the compaction process that forces the sediment grains closer together and squeezing an excess amount of the water.
How does a rock become a hard material over time?
- By the process of cementation when a dissolved groundwater mineral such as calcite (chalk) or iron oxide (rust) “glues” sediment grains together into solid rock.
What are some of the features of sedimentary rocks?
- Bedding: horizontal layering of sediments due to water or wind, and there are two types:
1) Graded bedding: particles tend to get heavier and coarser toward the bottom layers.
2) Cross-bedding: formed as inclined layers of sediments are deposited across a horizontal surface.
How do the ripple marks form?
- They form as sediment is moved into small ridges by wave action, wind, or river current.
- They are classified as symmetrical or asymmetrical.
How do we describe the shape of sediment grains?
- Jagged edge: broken pieces are at angular shape
- Rounded: individual pieces hit one another as edges break off, making them rounded.
What role does past life play in sedimentary rocks?
- Past life or remains of an organism known as fossils can be preserved in rocks as the sediments undergo the lithification process.
How are sedimentary rocks classified?
- By the way they form in terms of grain size, how they formed, and mineral content.
1) Grain size:
Coarse such as conglomerate
Medium such as sandstone with high porosity
Fine such as siltstone and shale
How do other sedimentary rocks form?
- They tend to form through chemical and biochemical processes based upon evaporation and precipitation of minerals.
1) Chemical sedimentary rocks: Crystal grains precipitate out of a solution at its saturation point and settles to the bottom into layers called evaporites such as gypsum or halite.
2) Biochemical sedimentary rocks: formed from the remains of past life such as those of shells that result in the formation of limestone that is made mostly of calcite.
Minerals: Metamorphic Rocks
How do metamorphic rocks form?
- They form from other rocks that undergo increases in temperature and pressure and to hydrothermal solutions deep in the earth, and result in different grades of metamorphism(high, low,&intermediate).
Does a rock always become metamorphic rock?
- No, some melt and return to magma; others partially melt allowing for crystals to rearrange themselves into new rocks forming those metamorphic rocks.
How do we classify metamorphic rocks?
- We classify them based upon their textures:
1) Foliated rocks: layers and bands of minerals such as gneiss or slate
2) Nonfoliated rocks: form with blocky crystal shapes such as marble or quartzite
How do area temperatures and distribution of minerals help scientists?
- Temperature range helps in locating valuable minerals such as garnet and talc.
- Distribution helps to explain the historical change of an area.
What are the three types of metamorphism?
- Regional metamorphism: Changes in minerals and rock types as well as folding and deforming of the rock layers
- Contact metamorphism: This occurs when molten material at high temperature and medium pressure comes in contact with a solid rock.
- Hydrothermal metamorphism: This happens when very hot water reacts with a rock and changes its chemical and mineral composition.
Note that valuable ore deposits of Au, Cu, Zn, W, and Pb are formed this way as well as sulfides such as galena and pyrite and iron ores such as hematite and magnetite.
How do these rocks play a role in our daily lives?
- Cooking (salt)
- Trade (gold & silver)
- Construction (marble & slate)
- Energy (fossil fuels)
- Cosmetics (dentistry)
Note that coal under high temperature and pressure changes to graphite (“lead” in pencil)
****Summarize your study of the minerals and rocks through a drawing of the rock cycle****