Crystallographic axes
The crystallographic axes intersect at the origin. they are useful for defining
the position of any face in space by the intersepts that the plane makes on
three mutually perpendicular lines called axes. Different crystals have axes of
different lengths. The axis which runs from front to back is called a axis,
the axis which runs from right to left is called b axis and the
one which runs from top to bottom is called c axis. Some crystals
have two axes of equall length and third one is of larger or smaller length. In
such crystals the axes of equall length are called a1 and a2 and
the third axes of different length ( which is vertical ) is called c. In soem
other crystals like cube all the three axes are of equall length and are calles a1(front
to back) , a2 ( right to left) and a3( top to bottom).
One end of each axis is positive and other is negative. Front end of a is
positive. Right end of b is positive and the top end of c is positive. The angle
between the a and b is called gamma, the angle between b and c is called alpha
and the angle between and c is called beta.