Native elements and sulphides - CH 19 and 20)
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Mineral class is defined by...
A single element
are native elements common or uncommon in earths crust?
what is special about native elements, when did they form?
what is the typical way in which the atoms are arranged?
Uncommon, and valuble (gold, silver, diamond)
amongst the earliest minerals to form in the solar system during planetary differentiation
typical cubic close packing with metallic bonding
What is a chondrite? what does it contain?
What is the matrix of the chondrites?
meteotires from unmelted asteroids; they are cosmic sediments composed of particules that were present in the solar nebula
contain: grains of Fe-Ni metals + CAl (calcium-aluminium rich inclusions)= the first solids to form in the solar nebula
Chondrules: milimetre sized spheres that are solidified droplets of silicate magma.
Matrix: presolar grains, solar nebular grains, organic materials
What are presolar grains?
metlas or non metals?
what minerals do they consists of?
Miniscule mineral grains found in the matrix of chondritesl grains are typically submicrometer in size - which are incredibly hard to separate.
Native elements (diamond-graphite), oxides(corundum), silicates
What is silicon carbide?
Moissanite (SiC) is classified as native elements - similar structure to diamond (colvalent bond) 250 polymorphs
What happened in the age of eath 4.567 Ga?
Dense metallic iron settles to core mantle crystallizes from a magma ocean- about 200 minerals formed
Differentiation of the earth:
earth is highly ___1___with a metallic core surrounded by a ___2_ __3___ mantle and it's crust
Core formation occured _4__million years after the beginning of the __5____ ___6___
- 1- differentiated
- 2-rocks, 3 solicate
- 4- 30
- 5- solar 6,system
differentiation of earth
early earth has a deep ___1__ __2___ heated by impacts and decay of short lived ___3____
arriving planetesimals disaggregated on impact and their metal components (mostly 4___) fell tghrough the molten ___5__ocean and underlying solid(but pastic) __6___ ____
- 1,2-magma ocean
- 3 radionuclides
- 6- silicate shell
represent the cores of __2__?
contain metallic iron and 10-20% nickel and represent the cores of asteroids
what crystal arrangement and elemtns ?
exsolved or sepataed from a single crystal of ____?
what are stony iron meteroites (1%)?
- Kamacite - body-centered cubic (Fe-Ni)
- exsolved or separated from a single crystal of TAENITE
- stony iron meteories
- -impacted - generated mixtures
- -pallasites, olivine metal mixtures
Sulphur metal bonds are ____% ionic?
Importance of sulphide minerals (3)
- ores - metals for society
- acid rock drainage or Acid mine drainage (sulphides=reactive)
- Geomicrobiology - extremophile metabolize sulphide
Cation and anions of each of the sulphides
- Cu2+ + S2-
- Mo4+ + S2-
- 2Cu+ + S2-
-isostructural with ___?
-substitution of ___ possible
- -isostructural with halite
- -Cubic closest packing
- Substituion with Fe2+ possible (over 40%)
- what does pyrrohotites magnetism depend on?
the metal/sulphur ratio
Structure dervided from ____ by replacing Na+ with Fe 2+
sulphur forms _1__bonded S2 pair (S22-) that occupy the Cl position in halite
Each Fe coordinated with __2__ S atoms and each S atom bonds with _3_ Fe
What minerals formed prior to the begining of the solar system and where are the found?
diamond, graphite, silicon carbide
found as microscopic grains in chondrititc meteorites
what defines a class of native elements?
defined by a single element abd subdivided into metals, semimetals and non metals
what evidence is there that early planetary bodies had iron rich-cores?
what are polymorphs of iron which are stable at temperatures and pressures of earths core?
HCP above 15 GPa
what is electrum?
Electrum is a naturally occurring alloy of gold and silver, with trace amounts of copper and other metals
how is sulphur bonded?
deformed rings of 8 covalently bonded S atoms from an S8 Molecule held together by van der waals bonds.
6 most abundant sulphide minerals
which composition and structure of pyrrhotite is magnetic? why?
Most common occuring is Fe7
- The ferromagnetism which is widely observed in pyrrhotite is therefore attributed to the presence of relatively large concentrations of iron vacancies (up to 20%) in the crystal structure. Vacancies lower the crystal symmetry. Therefore, monoclinic forms of pyrrhotite are in general more defect-rich than the more symmetrical hexagonal forms, and thus are more magnetic
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