Mica  

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

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/(g•K)		0.88
Thermal conductivity perpendicular to cleavage plane	W/(m•K)	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.