introduction to crystallography
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This ppt useful crystallography introductionTRANSCRIPT
Crystallography and Mineralogy
Dr.B.GURUGNANAMProfessor and HeadCentre for Applied Geology GRI-DU
Mr.K.KALAIVANANResearch ScholarCentre for Applied Geology GRI-DU.
Introduction to Crystallography
What is crystallography?
CRYSTALLOGRAPHY is simply a fancy word meaning "the study of crystals“
• The study of crystalline solids and the principles that govern their growth, external shape, and internal structure
• Crystallography is easily divided into 3 sections - geometrical, physical, and chemical.
Definition of crystal
A CRYSTAL is a regular polyhedral form, bounded by smooth faces, which is assumed by a chemical compound, due to the action of its inter atomic forces, when passing, under suitable conditions, from the state of a liquid or gas to that of a solid.
Crystalline and Amorphous
• (In Greek amorphous means “formless”) do not have overall regular internal structure; their constituent particles are arranged randomly; hence, they are isotropic, have no symmetry, and cannot be bounded by faces.
• Particles are arranged in them in the same way as in liquids; hence, they are sometimes referred to as super cooled liquids.
• Examples of amorphous substances are glass, plastics.
• In distinction to crystalline substances, amorphous ones have no clearly defined melting point.
Cont…
• Comparing curves of cooling (or heating) of crystalline substances and amorphous substances, one can see that the former has two sharp bend-points (a and b), corresponding to the beginning and end crystallization respectively, whereas the latter is smooth
Curve of cooling of a crystalline subsatnce
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Curve of cooling of amorphous substances
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ab
Symmetry
Symmetry map be defined in rotation to (i) Plane of symmetry
• Divided a crystal into two equal half • Mirror plane
(ii) Axis of symmetry • Parallel to the edge of intersection of
two crystal faces.• Binary, trigonal, tetragonal, hexagonal
(iii) Centre of Symmetry• Centre of symmetry if an imaginary
line passing the centre
Classification of crystals
• Classification of crystals according to the degree of crystallization
• Euhedral crystals• Subhedral crystals• Anhedral crystals
Euhedral Crystal Subhedral Crystal Anhedral
Crystal
Crystallographic forms
1- PedionIt is an open form made up of a
single face
Cont…
1- PinacoidIt is an open form made up of two
parallel faces
Basal Pinacoid
Side pinacoid
Front Pinacoid
Cont…
3- Dome
It is an open form made up of two nonparallel faces symmetrical with respect to a symmetry plane
4- Sphenoid
It is an open form made up of two nonparallel faces symmetrical with respect to a 2-fold or 4-fold symmetry axis
Cont…
5- Disphenoid
It is an closed form composed of a four-faced form in which two faces of the upper sphenoid alternate with two of the lower sphenoid.
Cont…
6 -Bipyramid
It is an closed form composed of 3, 4, 6, 8 or 12 nonparallel faces that meet at a point
Orthorhombic bipyramedDitetragonal bipyramid
Tetragonal bipyramid
Dihexagonal bipyramid
Hexagonal bipyramid
Cont…
7- PrismIt is an open form composed of 3, 4, 6, 8 or 12 faces, all of which are parallel to same axis.
Orthorhombic prism Tetragonal prism
Ditetragonal prism
Hexagonal prismDihexagonal prism
Cont…
8- Rhombohedron
It is an closed form composed of 6 rhombohedron faces,
9- Scalenohedron
It is an closed form composed of 12 faces, each face is a scalene triangle. There are three pairs of faces above and three pairs below in alternating positions
Crystal Habits
The term "crystal habit" is used to categorize the appearance, shape, and size of a crystal, and identify its unique growth characteristics that result from its crystalline structure and growth environment.
1. Crystal Twinning ( two individual crystals share some of the same crystal lattice points)
2. Growth Conditions (heat, pressure, and space)
3. Trace Impurities (present during crystal formation)
Crystal Habits
Crystal Habits
Crystal Habits
Crystal Habits
Crystal Habits
Crystal Habits
Crystal Habits
Crystal Habits