4: Minerals & The Rock Cycle Flashcards
What is a mineral?
A mineral is the building block of rocks, defined as:
“A structurally homogeneous solid of definite chemical composition, formed by the inorganic process of nature”
If you look at granite, you will realize that the granite “rock” is a aggregate of varying portions if different minerals (quartz, Feldspar, etc.)
What are the 6 things needed to qualify as a mineral?
- naturally Occurring
(lab made diamonds are not technically minerals) - Inorganic
(Coral and stuff, though made of minerals, are not technically minerals) - Solid
(lava is not a mineral) - Has Crystalline Structure
(Obsidian and opal are mineraloids since they don’t have a rigid repeating mineral structure like diamond) - Consistent Chemical Composition
(AKA, must have a chemical formula) - Physical properties reflect composition and crystalline structure
(AKA each mineral has a set of consistent physical properties)
How do you determine atomic number and mass?
Atomic number: number of protons
Atomic mass: Number of protons and neutrons
Talk about the types of bonding in minerals:
Ionic bonds: ion donates one or more electrons to another ion of opposite charge (think table salt)
- very low hardness
Covalent bonds: ions share one of more electrons
- super strong, think diamonds
Metallic bonds: A weak covalent bond that occurs in metals
Van der Waals: weak bond from slightly polarized atoms
(graphite is this bond. The sheets are bonded by this and come off easily, letting us write!)
Explain the crystalline structure of minerals:
minerals form a crystal structure, aka a repeated 3D arrangement of atoms
- A mineral’s crystal form (its regular geometric shape) is the external expression of its internal crystalline structure!
What are the 4 main ways minerals form?
- Cooling / crystallization from magma
- small crystals = cool quick
- Large crystals = cool slow - precipitation from fluid
(lake evaporates and leaves behind minerals) - Chemical changes from heat and pressure
(new minerals that are more in equilibrium with the new T and P can grow) - Precipitation from biogenic activity (biomineralization)
(Minerals must be inorganic, but organic stuff can make inorganic stuff. Coral isn’t a mineral, but coral reefs are made of CALCITE, a MINERAL!)
How do we identify minerals through “observable” physical properties? (6)
- Color
- Lustre: (metallic, non-metallic)
- Streak: powder form
- Hardness
- Cleavage: tendency to break along weak planes reflecting atomic structure
- Fracture: no cleavage (irregular, fibrous, etc.)
How do we identify minerals by other properties? (6)
- Reaction to Acid
- Magnetism
- Specific Gravity: weight ratio of mineral to water
- Taste
- Radioactivity
- Habit: general appearance of mineral, requires a large sample size
Where are most minerals found? How are mineral grouped?
IN the lithosphere
They’re grouped based on their anions (negatively charged ions)
What are the 4 elements that make up the majority (>90%) of earth’s composition?
Iron
Oxygen
Silicon
Magnesium
What are silicate minerals?
Silicate minerals are classified based upon the arrangement of their silicon-oxygen tetrahedra, which controls mineral properties
Silicates are divided into 2 catagories:
Mafic: Dark, High proportion of Fe and Mg
Felsic: Light, high proportion of silicon
Silicates are one third of all know minerals, but make up 90-95% of the crust
Anion: Silica Tetrahedron (SiO4 4-)
What does mafic / felsic mean?
mafic = dark silicates (high propertion of Fe, Mg)
Felsic = light silicates (high propertion of silica)
The more Mafic something is, the higher density
The more Felsic something is, the lower density
Where are silicate minerals located?
Silicate minerals dominate the mantle and crust
- The least dense silicates make up the crust
- The most dense silicates occupy the mantle
Major example of carbonate? What’s it useful for?
Anion: Carbonate ion
(Co3 2-)
Calcite - primary component of limestone and marble
- relative hardness 3
- Used in materials, cement, paint, abrasives, aggregative, etc.
How do sinkholes develop? (related to carbonate minerals)
Water fills a cavity below ground by eroding limestone (carbonates)
Erosion - Ground above water erodes and eventually reveals hole
Groundwater withdrawal - water goes away, hole collapses.
Surface loading - Too much weight above hole
