S & R Optic GmbH
Enabling Crystal Optics Solutions

Mica  

Properties of Mica

Mica is a group of naturally occurring minerals which cannot be grown artificially.
The group consists of:



For optical applications, only Muscovite is useful and is then simply called mica.



Mica can be cleaved to produce thin sheets which are somewhat flexible but mechanically stable.Depending on the raw material used and on the technical expertise of the cleaver, the sheets will be less or more suitable for optical applications.

Some facts about mica:

  • Optical characterization of raw mica is difficult and almost impossible.

  • Procurement of raw mica depends on excellent and long-lasting customer-supplier relationships.  

  • Cleaving of mica is a process which requires superb human experience.

  • Handling, and especially coating, of cleaved mica sheets is delicate.

  • Once cleaved, the thickness of mica sheets cannot be adjusted any further selection from stock material may be necessary.


Natural Mica Properties: Muscovite  

Property

 Unit

 min.

 typ.

 max.

General

 

 


 

Colour



ruby, green, white


Crystal structure



monoclinic


Cleavage



basal, eminent


Water of constitution

%


4.5


Moisture absorption



very low


Maximum operating temperature
without decomposition

°C

400


500

Mechanical

 

 


 

Density

g/cm³

2.8


3.1

Hardness - Mohs


2.0


2.5

Tensile strength (approx.)

GPa


0.17


Shear modulus

GPa

0.22


0.26

Compressive strength

GPa

0.19


0.28

Modulus of elasticity

GPa

140


210

Thermal

 

 


 

Specific heat

J/(gK)


0.88


Thermal conductivity
perpendicular to cleavage plane

W/(mK)

0.3

0.5

0.7

Coefficient of thermal expansion
perpendicular to cleavage plane
parallel to cleavage plane

 



 

Calcining temperature

°C

700


800

Melting point

°C

700


1000

Electrical

 

 


 

Dielectric constant


6


7

Apparent electric strength
(RMS @ 15 °C,  25 - 75 µm thickness)

kV/mm

120


200

Apparent electric strength
(RMS @ 15 °C, 250 - 1250 µm thickness)

kV/mm

40


80

Dielectric loss (power factor) (@ 15 °C)


 


 

Volume resistivity

Ω•m

 

 

 

Optical

 

 


 

Optic axial angle (2V)

degree

38


47

Orientation of optic plane to plane of symmetry



perpendicular


Refractive index nα


1.552


1.576

Refractive index n


1.582


1.615

Refractive index n


1.587


1.618

Maximum birefringence


0.035


0.042

Dispersion



r > v, weak


 

The information contained herein is typical for muscovite mica. As with all naturally occurring materials, mica properties may vary slightly. Consequently S & R Optic does not make any warranties for any particular use or purpose.