Got some textbook questions here, need some help :) Give short definitions or ex

Question

Got some textbook questions here, need some help :)

Give short definitions or explanations of the following: What is a centre of symmetry? Why the symbol 2 does not appear in the 32 crystal classes? What is the form scalenohedron? What is the primitive circle on a stereogram? Using symmetry characteristics to define the seven crystal systems. Sketch the symmetry elements of class^-43m in stereographic projection, mark the poles to the {111} form, and name this form. Which crystal system the symbol 3/m belongs to and why? You can use a stereogram to illustrate What are pyroelectricity and enantiomorphism? What symmetry characteristics are responsible for each of these two properties? What are the Albite and Pericline twin laws? Explain why these two twin laws commonly occur together in microcline from granites.

Explanation / Answer

1.a. center of symmetry - is a point within a crystal which any straight line extends to a point on opposite surfae of the crystal at equal distance.

1.b. A 2-fold rotoinversion axis is symbolized as a 2 with a bar on top and it would be pronounced as "bar-2". But, since it is equivalent of a mirror plane, the bar 2 is rarely used.

1.c.The forming of continuous (ie.without a real break other than the transitional) deposition
in the first stage of crystallization appears to be preferentially forming scalenohedron, a nice twinned crystals and even some big fish tail looking one. called as scalenohedron crystals.

1.d.The Primitive Circle is the circle that srrouds the stereo net(Streographic network) .

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