Morphological and Optical Crystallography

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Morphological and Optical Crystallography

• GEOL 3055
• Robert B. Watts

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Introduction

• Two semester classes
• GEOL 3055 Morphological and optical
  crystallography
• GEOL 3056 Crystal chemistry and the geochemistry
  of mineral systems
• Usually these courses are known as
• Crystallography
• Mineralogy

Mineral Science
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Introduction

• 3 classes of substance (or matter) distinguished
• Animal organic
• Vegetable organic
• Mineral inorganic naturally occurring
  crystalline substances

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IntroductionKlein p.1-3

• Basic branches of science to study the Earth
  include
• Petrology - study of rocks in terms of mineralogy
  texture
• Sedimentology - rocks formed from pre-existing
  rocks
• Geochemistry - distribution migration of
  chemical elements in Earth
• Structural geology tectonics - description of
  rock deformation
• Geophysics including seismology - physical
  conditions of Earth
• Economic geology mineral deposits their
  genesis
• Environmental geology - applying geologic
  research to land use

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Introduction

• What is a mineral?
• Components of rocks
• Sand on the beach
• Salt in Cabo Rojo
• Nice crystals in museums
• Jewelry

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Introduction

• What is a mineral?
• A mineral is a naturally occurring homogeneous
  solid, with a definite (but generally not fixed)
  chemical composition, and an ordered atomic
  arrangement, usually formed by inorganic
  processes.
• 3800 minerals identified on Earth

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Synthetic minerals
Substances produced in laboratories are excluded
in the strict sense eg synthetic diamonds.
However, a lot of knowledge of minerals comes
from the manufacture of synthetic minerals.

• Hemley and his colleagues at the Carnegie
  Institution, Los Alamos (N.M.) National
  Laboratory.

HARD TO RESIST. When exposed to high heat and
pressure, single-crystal diamonds like this
synthetic gem become extraordinarily hard, a new
study shows.Carnegie Institution
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Synthetic diamonds

• Thus, pressure-cooking produces extremely
  resistant material.
• The new material is so hard that tools used to
  gauge hardness left no mark on several of the
  crystals.
• In fact, the researchers broke equipment worth
  about 10,000 in their attempts at measurement.
• Material may serve as anvils for high-pressure
  research, coatings for cutting tools and
  biomedical implants, and wafers for electronics
  operating under extreme conditions.

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Introduction

• Traditionally, minerals form inorganically
• Calcium carbonate (calcite) precipitation in
  water kettles sewer pipes
• BUT some exceptions
• eg CaCO3 where aragonite secreted by animal
  (mollusk) to form a shell
• Another organic example is Apatite Ca5(PO4)3(OH)
  secreted by human body to form bones teeth

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Other examples of organic minerals

• Pearl aragonite CaCO3
• Sulfur formed by bacteria in Sulphur Springs

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Introduction

• Hybrid example
• Oncolites precipitated in lake near Syracuse due
  to pollution (CaCl dumped in a lake), calcite
  precipitated around a nucleus such as charophytes
  of mollusks - referred to as mineral because they
  formed through natural processes

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Introduction

• A mineral is a naturally occurring homogeneous
  solid, with a definite (but not fixed) chemical
  composition, and an ordered atomic arrangement,
  usually formed by inorganic processes.
• Consist of a single solid substance, that cannot
  be physically subdivided into simpler chemical
  compounds
• So breaking it into smaller and smaller pieces it
  should still remain the same mineral.
• What looks homogeneous to the naked eye may b a
  fine intergrowth under the microscope.

Eg Perthite - intergrowth of 2 feldspars
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Introduction

• Note Solid excludes gas and liquid.
• Water is not a mineral, but ice in a glacier is.
  Ice in the refrigerator should be called
  synthetic.
• Mercury is not a solid, because it occurs
  naturally as a liquid, may be referred to as
  MINERALOID (mineral-like substance)

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Introduction

• A mineral is a naturally occurring homogeneous
  solid, with a definite (but generally not fixed)
  chemical composition, and an ordered atomic
  arrangement, usually formed by inorganic
  processes.
• All minerals can be expressed by a chemical
  formula
• Quartz - SiO2
• Halite NaCl

Pure substances-defined chemical composition
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Introduction

• In reality, most minerals do not have such a
  well-defined chemical composition.
• Example dolomite CaMg(CO3)2,
• but in nature Mg is usually partially substituted
  by Fe and Mn
• So although the formula implies
• 1Ca 1 Mg and 2 CO3 ions.
• It is more realistic to write Ca(Mg,Fe,Mn) (CO3)2

So not a fixed composition!
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Introduction

• A mineral is a naturally occurring homogeneous
  solid, with a definite (but generally not fixed)
  chemical composition, and an ordered atomic
  arrangement, usually formed by inorganic
  processes.
• An internal structural framework of atoms/ions in
  regular geometric pattern or crystal lattice
• Thus a mineral is a crystalline solid
• Again, there are exceptions to this rule,
• Volcanic Glass is amorphous example of
  mineraloid

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History of Mineralogy

• Early use of minerals in
• Cave paintings
• Use of hematite (Fe2O3) as red pigment
• Use of manganese oxide (MnO) as black pigment
• Flint (amorphous silica) commonly used in Stone
  Age as arrowheads

Lascaux, France, from National Geographic 1988
October
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Introduction

• Egyptian tombs and pyramids, use of gold,
  malachite, lapis lazuli, garnet.

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Introduction

• Theophrastus (372-287 BC)
• First written work on minerals
• Plinius first century AD
• During the middle ages no new contributions, few
  factual acounts.

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Introduction

• Gregorius Agricola (German physician) published
  De Re Metallica in 1556
• Detailed account of mining practices

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Introduction

• First major contribution by
• Nicolaus Steno (Niels Stensen)1638-1686
  Copenhagen, Denmark.
• Angles between the corresponding faces of a
  quartz crystal remained constant despite their
  differences in size, origin or habit.

Fig. 1.4
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Introduction
Fig. 1.5
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Introduction

• One century later, Carangeot 1780 invented the
  contact goniometer to measure interfacial angles

• Rome de lIsle in 1783 made angular measurements
  on crystals and confirmed the Law of the
  Constancy of interfacial angles of Steno.

Fig. 1.7a
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Introduction

• One year later, 1784 Rene J. Hauy showed that
  crystals were built by stacking together tiny
  identical building blocks. These blocks known as
  integral molecules.

Garnet dodecahedron
Fig. 1.6
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Introduction

• 1809, Wollaston invented the reflection
  goniometer which allowed for highly accurate and
  precise measurements of crystal faces. Turned
  crystallography into an exact science.

Fig. 1.7c
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Introduction

• From 1779-1848 Berzelius (Sweden) and his
  students studied mineral chemistry and developed
  the principles of the chemical classification of
  minerals.
• 1815 the Frenchman Cordier studied mineral
  fragments in water --- immersion method. Useful
  technique for optical mineralogy.
• 1828 Scotsman William Nicol invented a polarizer
  that permitted the systematic study of the
  behavior of light in crystals. A polarizing
  microscope is powerful tool for mineral
  identification.

Fig. 1.8
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Introduction

• 20th century X-ray crystallography
• 1912 - von Laue discovered crystals can diffract
  X-Rays

Sir William Henry Bragg (1862-1942)
Sir William Lawrence Bragg (1890-1971)

• 1914 Father Son Bragg do earliest crystal
  structure determinations win Nobel Prize in
  Physics

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Q. So what is an X-Ray? A. Form of
electromagnetic radiation of short wavelength
1nm (1 x 10-9 m) X unknown - X-rays are
emitted from an excited atom when bombarded in a
vacuum tube with high-voltage electrons. Distinct
ive X-rays vary in intensity wavelength and are
different from element to element - useful for
I.D. Like other forms of electromagnetic
radiation they show wave characteristics of
interference, diffraction polarization.
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Q. So what is X-Ray Diffraction?
Diffraction is the bending, spreading and
interference of X-rays when they pass by an
obstruction or through a gap - this occurs in any
type of wave. X-rays can be diffracted from the
repeated patterns of atoms characteristic of
crystalline materials. Max von Laue discovered
that if the wavelength inter-atomic distance
are roughly the same then a diffraction pattern
could be formed.
Diffraction - after passing through an aperture
diffracted waves interfere with each other to
produce zones of reinforcement weakening.
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Diffractometer with goniometer
Diffractogram
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Introduction

• 1960 -- the electron microprobe permitted the
  study of minerals on a microscale. This uses a
  beam of electrons (5?m) in diameter to form a
  visual image and analyse X-rays of elements
  present.
• 1970 High-resolution transmission electron
  microscopy (HRTEM)

Cameca microprobe at UPR
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Guallatiri Volcano North Chile
Petrologic study of Guallatiri Dome samples using
Electron Microprobe
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Introduction

• Naming of minerals
• Some examples
• Albite from albus (Latin) white
• Rhodonite from rhodon (Greek) pink
• Chromite from the content of Chromium
• Magnetite for its magnetic property
• Franklinite after locality, Franklin, New Jersey
• Sillimanite after professor Benjamin Silliman of
  Yale University (1779-1864)

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Introduction

• No logical way to name minerals.
• Usually the discoverer or first describer gives
  the name.
• This name is either accepted or not by the
• Commission on New Minerals and New Mineral Names
  of the International Mineralogical Association
  (CNMNMNIMA)

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