Orthorhombic system


Crystallographic Axes

All the crystal forms of orthorhombic system can be referred to three axes of equal lengths which intersect at right angles. These are denoted by a, b and c. The a axis runs from front to back, b runs from left to right and c runs from top to bottom. The values of angel alpha, beta and gamma is 90 degree.

Symmetry Classes - 

The symetry classes which belong to this system are :

Baryte Type or Orhormoobic-bipyramidal Class

Baryte Type Class

This class takes it's name from the common mineral Baryte (BaSO4), which belongs to it.

Symmetry

The symmetry of this class can be deduced from the typical form cube.

Planes 3 - Axial.

Axes  3 - 3 of  two fold.

A centre of symmetry.

Forms

1) Basal or c Pinacoid - It is an open form having two face. Each face cuts only the c axis and is parallel to horizontal axes. The Miller symbol of the form is (001).

2) Front or a Pinacoid - It is an open form having two faces. Each face cuts only the a axis and is parallel to b and c. It's Miller symbol is (100).

3) Side or b Pinacoid - It is an open form having 2 faces. Each face cuts only the b axis and is parallel to a and c. It's Miller symbol is (010).

4) Prism of third order - It is also an open form having 4 vertical faces. Each face cuts a and b axis and is paralle to c axis. It's Miller symbol is (110).

5) Prism of second order or Dome - This is an open form of 4 faces. Each face is parallel to b axis and cuts a and c axis. It's Miller symbol is (101).It is also known as macrodome.

6) Prism of first order or Dome - This is an open form having 4 faces. Each face is parallel to a axis and cuts b and c axis. It's Miller symbol is (011).

7) Bipyramid - It is a closed form having 4 faces face cuts all the three axes at unit distance. It's Miller symbol is (111).