Minerals: Earth Materials Flashcards
What is the solid Earth made of?
Rocks like basalt, granite and sandstone make up the Earth
Rocks are made of minerals. What are they?
the smallest homogenous units that the Earth can be physically broken into
What are Minerals made of?
A single element
OR
2 or more elements combined to form a chemically stable and electrically neutral compound
Why are minerals important?
the building blocks of rocks
important resources - integral to our culture since early humans, store elements necessary for life
critical to determining the history of our planet - form in very specific conditions and environments
minerals are often important evidence in crime scene investigations
All solid Earth processes involve growth and destruction of …
minerals
What is a mineral? (definition)
Naturally occurring Inorganic (not soft parts of organisms, plants) Ordered internal crystalline structure Fixed chemical composition Homogeneous solid
Graphite and Carbon are both pure carbon, so why are they so different?
differ in internal structure (how the C atoms are arranged)
Graphite - Sheets
Diamond - Tetrahedral formation
Why do different elements combine to form minerals?
To become stable: for atoms to have a full outermost electron shell
How do different elements combine to form minerals?
Lose electrons -> gain net positive charge (become a cation)
OR
Gain electrons -> become a negatively charged ion (anion)
What are ions?
Charged atoms
what is an Anion?
Negatively charged ion - atom has gained electrons
what is a cation?
Positively charged ion - atom has lost electrons
What are the two types of bonding?
Electron transfer: ionic bonding e.g. NaCl halite
Electron sharing: covalent bonding
what is the composition of the Earth’s Crust?
Mostly Si and O
Remainder: Al, Mg, Na, K, Fe
Only ~20 minerals account for most of the crust:
Rock-forming minerals
Mainly silicates (Feldspars, quartz, micas, olivine, pyroxenes, amphiboles, clays)
Also carbonates
What are the silicate mineral groups?
different arrangements of silicate (SiO4) tetrahedra
each mineral group has different characteristics
What is an example of an isolated tetrahedra silicate mineral?
olivine
garnet
What is an example of a chain silicate mineral?
pyroxene
What is an example of a double chain silicate mineral?
amphibole
What is an example of a sheet silicate mineral?
mica
What is an example of a 3D framework silicate mineral?
quartz
What is the mineral composition of olivine?
Mg2SiO4 or Fe2SiO4
What is the mineral composition of quartz?
SiO2
Why do minerals have colour?
Interaction of light with ions and their bonds
Different ionic substitutions
Chemical impurities
what are mineral properties dictated by?
composition, bonding, and structure
what are the properties of minerals?
Crystal structure Colour and streak Lustre (metallic, nonmetallic) Hardness: Moh's scale Cleavage Fracture Specific gravity Taste Magnetism Reaction with acid
what are the requirements to make a mineral?
- Right elements/ions must be available e.g.magma, Si, O, Al,Fe,Mg, Ca, etc seawater Cl,Na,SO4, Mg, Ca, CO3 etc
- Right temperature e.g.olivine: highT, clay: low T
- Right pressure e.g. garnet: moderate T and P
How do conditions for minerals change in the Earth?
Increase depth of a mineral -> enormous increases in pressure and temp
e.g. 3 km burial: increases P by 1000 atmospheres (bars)
What causes changes in earth conditions?
Tectonic processes (burial and exhumation)
Magmatism
Weathering
Why do basalt/gabbro rocks formed at MORs turn into eclogite in subduction zones?
Basalt/Gabbro -> Eclogite
transformation of minerals due to increased depth (subduction) [P, T increases]
Mineral changes help drive …
subduction and move plates
How are new elements introduced?
Weathering (e.g., oxidation)
Presence of aqueous fluids/gases
E.g., Hydrothermal Metamorphism mid-ocean ridges: interaction with H2O (added)
What hydrous minerals does Pyroxene (no h2o) turn into?
chlorite
epidote
actinolite
what are the processes for making a mineral?
Crystallisation from cooling molten rock -> minerals in igneous rocks
Increased pressure/temperature -> new minerals, in metamorphic rocks
Weathering -> new minerals formed by alteration of existing ones
Precipitation from aqueous fluids/gases
Growth of minerals in shells/teeth/bones
what does it mean for a mineral to be metastable?
Many deep Earth minerals exist at surface out of their stability limit - thus they are metastable
how are diamonds carried to the surface?
rapidly in host kimberlite magma
