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Introduction to Crystallography
Crystallography is the study of crystals, their growth, structure, and properties. A crystal is a solid with a regular, repeating internal structure at the atomic scale. Crystals have long-range order and are bounded by smooth, flat faces. Crystals can be classified based on their degree of crystallinity as euhedral, subhedral, or anhedral. Crystals exhibit symmetry properties like planes, axes, and centers of symmetry. They can also take on specific crystallographic forms like prisms, bipyramids, and rhombohedra. A crystal's habit describes its external shape and is influenced by its structure and growth conditions like temperature, pressure, and impurities.
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Introduction to Crystallography
- 1. Crystallography and Mineralogy Dr.B.GURUGNANAM Professorand Head Centre for Applied Geology GRI-DU Mr.K.KALAIVANAN Research Scholar Centre for Applied Geology GRI-DU.
- 2. Introduction to Crystallography Whatis 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.
- 3. Definition of crystal ACRYSTAL 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.
- 4. 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.
- 5. Cont… • Comparing curvesof 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 0 10 20 30 40 50 60 050100 time, min To a b
- 6. Symmetry Symmetry map bedefined 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
- 7. Classification of crystals •Classification of crystals according to the degree of crystallization •Euhedral crystals •Subhedral crystals •Anhedral crystals Euhedral Crystal Subhedral Crystal Anhedral Crystal
- 8. Crystallographic forms 1- Pedion Itis an open form made up of a single face
- 9. Cont… 1- Pinacoid It isan open form made up of two parallel faces Basal Pinacoid Side pinacoid Front Pinacoid
- 10. Cont… 3- Dome It isan 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
- 11. Cont… 5- Disphenoid It isan closed form composed of a four-faced form in which two faces of the upper sphenoid alternate with two of the lower sphenoid.
- 12. Cont… 6-Bipyramid It is anclosed form composed of 3, 4, 6, 8 or 12 nonparallel faces that meet at a point Orthorhombic bipyramed Ditetragonal bipyramid Tetragonal bipyramid Dihexagonal bipyramid Hexagonal bipyramid
- 13. Cont… 7- Prism It isan 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 prism Dihexagonal prism
- 14. Cont… 8- Rhombohedron It isan 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
- 15. 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)
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