Скачать или смотреть Crystallography: Hexagonal System Beryl Type

Hexagonal System Baryte type explained with the help of glass models, wooden models and detail explain is given on black board. Explain Crystallographic axes, Elements of symmetry Forms and Indices.

HEXAGONAL SYSTEM
Type: Beryl

CRYSTALLOGRAPHIC AXES:
Unlike other crystallographic systems, Hexagonal system has four crystallographic axes, the c- axes running from top to bottom. It may be longer or shorter than other 3 axes which are horizontal. The three horizontal axes are equal in length and make an angle of 1200 with one another. These axes are denoted as a1, a2 and a3.
ELEMENTS OF SYMMETRY:

(1) Planes of symmetry – 7 (6V, 1H)
(2) Axis of symmetry – 7 (62, 16)
(3) Center of symmetry – Present

FORMS:

(1) Basal pinacoid :- It consists of two similar faces, index face cutting c axes and remaining parallel to the horizontal axes (0001)

(2) Hexagonal Prism of 1st order :- It consists of 6 similar vertical faces, index face cutting a1 axes and negative end of a3 axes at equal distance while remaining parallel to a2 and c axes (1010)

(3) Di-Hexagonal Prism :- It consists of 12 similar vertical faces, index face cutting all the three horizontal axes at unequal lengths and a3 axes at negative end and remaining parallel to c axes (hik0)

(4) Hexagonal Pyramid of 1st order :- It consists of 12 inclined faces, index face cutting a1 and negative end of a3 axes and c axes at unit distance and remaining parallel to a2 axes (10Ī1)

(5) Di-Hexagonal Pyramid :- It consists of 24 inclined faces, index face cutting a1, a2, negative end of a3 axes and c axes at unequal distance (hikl)

RULE FOR HOLDING POSITION

The axis of six fold symmetry should coincide with the c axes.
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