The monoclinic system includes all those forms that can be referred to three crystallographic axes which are essentially unequal in length and further that can be of these is always inclined.
All the three axes are unequal, they are designated by the letters a, b and c. The c axis is always vertical. The inclined axis is a- axis. It is inclined towards the observer and is also referred as clino axis.
Normal class symmetry
There are three symmetry classes placed in monoclinic system. The symmetry of the normal class is as given below:
a) Axis of Symmetry
1 axis of two fold symmetry only
b) Planes of symmetry
1 plane of symmetry only. And a centre of symmetry. The plane of symmetry is that plane which contains the crystallographic axes a and c
The common forms of this system are
it is an open from of two faces, each face being parallel to the two axes and cutting the third at a unit length .Three pinacoids are distinguished in the monoclinic system.
A dome is also form of two faces, each face meeting the vertical axis and one of the other two axes. It is a parallel to the third axis. Two types of domes are recognized:
Orthodome ii) Clinodome
There are three types of prisms is there;
i) Unit prism ii) Orthoprism iii) Clinoprism
These are closed forms and in these each face meets all the three axes.
i) Unit pyramid
The internal atomic arrangement of a mineral is manifested outwardly by development if geometrical shapes or crystal characters. The forms may be following three types:
i crystallized - When the mineral occurs in the form of well defined crystals.
ii Amorphous - When it shows absolutely no signs or evidence of crystallization.
iiiCrystalline - when well-defined crystals are absent but a marked tendency Towards crystallization.
Some of the special properties are mentioned below:
Some minerals are highly magnetic,e,g magnetic, whereas few others may be feebly magnetic like spinals and tourmaline.
Some minerals an electric charge may be developed by heating in some others same effect results by applying pressure.
This term express property of some minerals to emit light when exposed to radiation.
It is similar to fluorescence in essential character but in this case light is emitted not during the act of exposure to radiation but after the substance is transferred rapidly to dark place.