The formulas may be complicated as they are made up of many things.
Commas in the parentheses means elements can substitute for one another.
Minerals are inorganic -> they have no C-H bonds.
Minerals are crystalline solids -> they have an orderly pattern in their molecules.
What is a crystal?
- A single, continuous piece of a crystalline solid
- Typically bounded by flat surfaces
- Has a simmilar apperence to scaffolding of a building (called a crystal lattice)
Add image from page 12 of lecture
page 15 symvols of key elements
Abundance of the elements
- In the crust: Osygen and silicon
- The whole earth: Oxygen and Iron
Atoms have a nucleus and an electron cloud.
The atomic number is the number of protons
The atomic weight is the number of protons + neutrons
Atomcs can gain or lose electrons andbecome ions.
Negativly charged are called anions.
Postiivly charged are called cations.
Bonding
Ionic bonding
When an atom is tranfered from to another
Covalent bonding
When an atom is shared between two atoms.
More stable than ionic bonds.
Silicates, the most common mineral group, contain the element silicon which forms covalent bonds with oxygen, called a silica tetrahedra.
Bond strength is dependent on direction -> causes some minerals to grow faster in one direction.
Polymorphs are minerals with the same chemical formula but different structures/bonds/properties.
- Sometimes cations of simmialr sizes and charges can substitute for each other!
- Saphires and rubies are the same mineral just with slightly different formulas
How do minerals form?
Solidifying from melted rock.
Precipitating from a solution.
Precipitating from a gas.
Biomineralization (An organism making minerals).
- Ex: shells produced by clams
Solid state diffusion (atoms that migrate from the crystal to form new minerals)
For a mineral to form, it needs a seed crystal.
A seed crystal is a tiny crystal that acts as a catalyst. Atoms attach to the seed’s outer surface and allows the seed to grow outwards.
Lack of space affects mineral growth.
Anhedral crystals are grown in tigh spaces and have no crystal faces.
Euhedral crystals are grown in an open cavity and have good crystal faces. This is also called a geode.
How do minerals break down?
Melting
Dissolving -> Solvents (usually water)
Chemical reactions -> Reactive minerals
Microbial metabolism -> Some microbes eat minerals for energy
How to identify minerals?
Common properties:
- Color
- Streak
- Luter
- Hardness
- Specific gravity
- Crystal habit
- Fracture or cleavage
- Magnetic
- Effervesence
Hardness:
- Uses the Mohs Scale (1-10 where 10 is the hardest)
- Strong covalent networks -> very hard (Ex: Diamond, quartz)
- Weak van der Weals bonds -> softest (Ex: Talc)
- If it doesn’t scratch the streak plate, it has a hardness of above 6.5
Clevage:
- Minerals break where their bonds are weakest
- Cleavage creates flat, shiny surfaces that are like steps
- If a mineral doesnt have cleavage, it will instead fracture.
Solubility
- Ionic lattices dissolve quickly in water (Ex: Halite, gypsum)
- Covalent lattices are much less soluable (Ex: Diamond, quartz)
Luster
- Free or mobile electrons -> shiny
- Silicates and carbonates -> glassy
- Nonmetalic lusters can be divided into: Silky, vitreous (glassy), satiny, resinous, pearly, earth, adamantine
Color
- Unrealiable because the same mineral can have many colors
- Malachites: Green
- Azurite: Blue
- Proustite: Red
Streak
- The color of the mineral in its powdered form
- Can be tested by dragging a mineral across an unglazed porcelin plate
- Ex: graphite from a pencil
- Ex: Hematite: Redish brown streak
- Ex: Gold (black streak) vs Pyrtie (gold streak)
Gravity
Crystal habit
- The shape of a single crystal
- Types: fibrous, wiry, dendritic, boladed, tabular, botryoidal, radiating needles, etc
Effervescence
- Reacting with an acid
- Useful for minerals
- Ex: Calcites will react will hydrochloric acid to produce carbon dioxide
- a lot more properties that are less common
Common Minerals
Silicates are most abundant and common in Earth’s crust.
To be continued...