Introduction
What’s the definition of a mineral ?
Definition of a mineral (Geology 101)
1) Naturally occurring solid
2) Inorganic
3) Definite Chemical Composition
4) Systematic internal pattern
- ordered Atomic Arrangement
Mineralogy (Gel 2130) definition of a mineral
A mineral is a naturally occurring homogenous solid
with a definite (but not fixed) chemical composition
and a highly ordered atomic arrangement.
A mineral is usually formed by inorganic processes.
1) Naturally occurring
-
Formed by natural processes (incl. kidney stones,
bones, siderite (FeCO3) that ppt in water pipes)
-
Synthetic diamonds, emeralds, rubies, etc.
are not minerals
-
Chemical compounds are not minerals even if
they have “mineral structures”. E.g. Calcium
Carbonate (CaCO3) added to your Cheerios
2) Homogenous solid
- cannot be subdivided into smaller components
(excludes perthite – Na-rich lamella in a K-rich
feldspar host)
-
fluids are not minerals – water, oil, gas, mercury
(mineral water)
-
Ice in a glacier is a mineral
3) Definite Chemical Composition
-
Quartz - SiO2 – pure substance
-
Dolomite – Ca,Mg (CO3)2
-
can also contain Mn, Fe, Sr that substitute for
similar sized and charged atoms
- Dolomite is better written Ca(Mg,Fe,Mn,Sr)(CO3)2
(within a range) – geothermometers and
geobarometers
-
If concentration of an element exceeds a specific
range we give mineral a new name
3) Definite Chemical Composition
-
If concentration of an element exceeds a specific
range we give mineral a new name
e.g. Siderite (FeCO3), Magnesite (MgCO3)…
-
Spinels XY2O4 where X = +2 , Y = +3
Spinel – MgAl2O4; magnetite Fe,Fe2O4
4) Systematic internal pattern (crystalline)
- ordered Atomic Arrangement
-
internal framework of atoms (ions) that are
arranged in a regular geometric pattern
-
if material has no structure is amorphous and
called a mineraloid (e.g. opal, limonite)
-
some materials can start off as minerals but the
atomic arrangement can be destroyed by
radiation to produce a metamict material (e.g.
allanite, zircon, many other radioactive minerals)
5) Inorganic processes – the usual case
-
Biogenic
Organic: carbonates (aragonite, calcite, vaterite)
phosphates
silica
sulfur
oxides (magnetite in bird brains)
History of Mineralogy
Early Humans – used hematite and psilomelane
to draw pictures in caves - (25,000 B.C.)
Bronze Age metallurgists (5,000 B.C.)
Egyptian Tomb paintings of smelting metals
Theophratus – (372-287 B.C.) – Greeks
Pliny (the younger) – (~100A.D.)
1556 – Georgius Agricola – De Re Metallica
- translated by Hoover + Hoover 1912
1669 – Nicolas Steno – noted that angles between
different faces were the same despite differences
in crystal size, origin, or habit
1780 – Carangeot – invented contact goniometer to
measure interfacial angles
(external morphology reflects internal structure)
1783 – Rome de l’Isle measured interfacial angles and
formulated law of constancy of interfacial angles.
1784 – Rene J. Hauy – developed the concept that
minerals were made from small building blocks.
- today = molecules forming unit cell.
1801 – He developed system indices for crystal faces
1809 – Wollaston - invented reflecting goniometer
and made crystallography an exact
science
1779 to 1848 – Berzelius – developed chemical
classification system for minerals
1815 – Cordier – started using the microscope to
study minerals and developed the immersion
(water + oil) methods for crushed minerals.
1828 – William Nicol – Developed the polarizing
tool (Nicol prism) for the optical microscope.
1912 – von Laue suggested that crystals would
diffract X-rays
- diffraction demonstrated by Friederich + Knipping
1914 – Bragg+Bragg – First determination of crystal
structure (Nobel prize in Physics)
1960’s – Computerized X-ray diffractometers
- Electron Microprobe
- Scanning Electron Microscope
1970’s - Transmitting Electron Microscope
1990’s - Ion Microprobe
What to learn from course
1)
2)
3)
4)
5)
Symmetry – classes
Miller Indices
Crystal Chemistry – what else fits in
Associations
Identification