in geology, a mineral is a naturally occurring ...geowords.com/p_/03b-ge101-minerals-3.pdf · in...
TRANSCRIPT
In geology, a mineral is a
naturally occurring, crystalline, and inorganic.
As a mineral is crystalline it will be a solid as no
liquid crystals occur in nature. A definite chemical
formula can be written for a crystalline material.
In geology, naturally occurring amorphous solids,
such as glass, and liquid materials of all sorts
such as lava and, at room temperature, mercury,
and water are not minerals.
Amalgams (mixtures) such as bronze and
portland cement are not minerals.
In geology, a mineral can be:
a native element that consists of
atoms of one element that are
chemically bonded (for example,
native sulfur)
or
a chemical compound that consists
of atoms of two or more elements
that are chemically bonded (for
example, calcite).
In geology, a mixture is one or more
atoms or compounds, or both, of
elements that are not chemically
bonded to each other. For example,
cement is not a mineral.
Native elements that occur as minerals
Native elements that occur as minerals
The only liquid elements at standard (room) temperature
and pressure are:
bromine (Br) and mercury (Hg).
Although, elements
gallium (Ga), rubidium (Rb), caesium (Cs),francium
(Fr) become liquid just above room temperature.
Gaseous Elements (stp) hydrogen (H), nitrogen (N), oxygen (O), fluorine (F),
chlorine (Cl)
and noble gases:
helium (He), neon (Ne), argon (Ar), krypton (Kr),
xenon (Xe), radon (Rn)
Some minerals contain only certain elements:
Halite - NaCl
Quartz - SiO2
Orthoclase - KAlSi3O8
Some minerals have a range of compositions:
Olivine - (Mg,Fe)2SiO4
Hornblende - (Ca,Na,K)2-3(Mg,Fe,Al)5(Si,Al)8O22(OH)2
Plagioclase - (Na,Ca)Al1-2Si3-2O8
Albite Anorthite
Amount of sodium and calcium Percentage of Albite (Ab) and
Anorthite (An)
Albite (Na100% , Ca 0% ) Al Si3O8 90-100% Ab ; 0-10% An
Oligoclase (Na90% , Ca10% ) Al1-2Si3-2O8 70-90% Ab ; 10-30% An
Andesine (Na70% , Ca30% ) Al1-2Si3-2O8 50-70% Ab ; 30-50% An
Labradorite (Ca70% , Na30% ) Al1-2Si3-2O8 30-50% Ab ; 70-50% An
Bytownite (Ca90% , Na10% ) Al1-2Si3-2O8 10-30% Ab ; 70-90% An
Anorthite (Ca100% , Na0% ) Al2Si2O8 0-10% Ab ; 90-100% An
Plagioclase - (Na,Ca)Al1-2Si3-2O8
Crystal forms (shapes)
cube octahedra blades hexagonal prisms
dodecahedra rhombohedra tetragonal prisms
Diffraction of an X-ray beam thorough a
crystal produces a (Bragg) diffraction
pattern spots on a screen due to
interference of overlapping X-ray waves..
Ball and stick model of halite
Packed ball
model of
halite shows
how the
different
sized ions fit
together in a
crystal.
In graphite, carbon atoms are covalently
bonded into sheets that are held
together by weak bonds.
Carbon is in group 4 of the periodic
table and so it has four electrons in
its outer shell. Three of these electrons
are used for covalent bonding in
the graphene sheet. The fourth electron
between the layers is delocalized.
It is a free electron and these free
electrons between the layers let them
slip and makes graphite a lubricant and
allows graphite to conduct
electricity and heat.
Sheet silicates
Sheet silicates
If an Al+3 is substituted for every 4th Si+4 in the tetrahedral layer,
this causes an excess -1 charge in each T-O-T layer. To satisfy
the charge, K+1 or Na+1 can be bonded between 2 T-O-T sheets
in 12-fold coordination.
For the trioctahedral sheet silicates this becomes Phlogopite
(Mg-biotite),
and for the dioctahedral sheet silicates this becomes Muscovite.
In a diamond, covalently bonded carbon
atoms are arranged in tetrahedra.
Even though diamond is the hardest
mineral it can chip and fracture in
normal day to day wear and tear.
Diamond is formed in the cubic crystal
system and has 4 perfect cleavage
directions. An experience diamond
cutter will look for the cleavage plane to
cleave a big diamond. The toughness
rating of diamond is only ‘good’ while
that of Jadeite Jade and Nephrite Jade
have a toughness graded as
Exceptional.
