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What are the Miller indices of all the faces of a simple cube? Use a well-labelled
drawing in your answer.
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• What is Steno’s Law? Use a
drawing in your answer.
- Steno’s Law – “Law of constancy of interfacial angles” states that the angles between corresponding faces are constant. E,g. Quartz has interfacial
- angles of 120 degrees.
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How many plane lattices are there in two dimensions
and how are they defined (axes and angles)?
In 2D dimensions there are two dimensions a and b and an angle γ. There are 5 plane lattices in 2D, which are square, rectangle, diamond, hexagonal and oblique
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• What is the difference between a unit mesh and a unit cell?
A unit mesh: shape that can be repeated by translation to fill space (square, hexagonal etc..)
A unit cell: volume outlines by lattice modes; simplest shape that can be translated in 3D to fill space
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• What is the relationship between plane lattices and Bravais lattices?
The 5 plane lattices can be repeated in 3Dto produce 14 different space lattices known as the Bravais Lattices, these 14 bravais lattice are divided in to 6 groups based on the shape of the unit cell
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What are the differences between point groups and space groups?
- Point groups represent the number of different combinations of symmetry around a point in three
- dimensions (reflection, rotation, inversion. They may be grouped into the 6 different crystal sytems based on unit cell geometry generated from the bravais
- lattices
- Space groups represent
- all the combinations of point symmetry with translational symmetry. This requires two additional compound symmetry operations – glides and
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• What is a glide plane? Use a diagram in your answer.
Translation followed by areflection in the mirror plane
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• What are quasi crystals and how is their internal structure different from regular crystals?
Quasi crystals present 3D symmetry that is strictly forbidden for crystals (e.g. 5-fold and 10-fold rotational axes). Internal structure is ordered but not periodic as it lacks symmetry.
- only known naturally occuring camefrom a meteorite - Icosahedrite
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Why are planes with low lattice-node density unlikely to be major faces in a crystal?
Crystal faces parallelto Q are less likely to develop or will be minor.
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• What is the meaning of using the following different notations when describing crystals: (001), [001], {001}
A cleavage (shown with thin lines)parallel to the (001) crystal face is identified as {001} cleavage. Use braces{ } to indicate cleavage or twin planes.
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• What is the Miller index when a crystal face is parallel to a crystal axis?
- The crystal faces (110), (1-10), (-110), and (-1-10)
- constitute a [001] zone because they
- intersect in edges parallel to
- [001 which is the zone axis
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What is the Law of COnstancy of interfacial angles?
The angles between corresponding faces are constant e.g. quartz has angles of 120 degrees between each face
-
What is the study of crystallography?
Thestudy of crystalline solids and the principals that govern their growth, external shape and internal structure.
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Primitive vs centered unit mesh?
- Primitive = lattice nodes only at the corners.
- Centered unit mesh = lattice nodes also occur in the centre
-
P =
C=
F=
I=
how many known crystals are there
- P= primitive
- C= face-centered
- I = body-centered
- F= Fully face-centered
= >4500
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What is an entantiomorphic crystal?
- Frorms lack of centre symmetry and mirrors so it is possibl to have left handed and right handed versions of the crystal
- - also means they have a screw axis
- -Common in QUARTZZZZ
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WHat is the law of Huay vs Law of Bravais?
Huay : Crystal faces make simple rational intercepts on crystal
Bravais: common crystal faces are parallel to the lattice planes that have high-lattice node density
-
PLANE "T" VS "Q"
- T = high lattice-node density = likely to be a crystal face
- Q= low Lattice-node density , likely not a common crystal face
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