Properties Units Muscovite Phlogopite
Color Ruby/ Green/ Amber/ Silver/Green
Density gm/cm3 2.6 – 3.2 2.6 – 3.2
Specific heat 0.21 0.20
Hardness Moh scale 2.8 – 3.2 2.3 – 3.0
Shore Test 80-105 70-100
Breakdown voltage KV/mm 120 – 200 –
Coefficient of expansion per  °C perpendicular to cleavage plane 9 x 10-6 – 36 x 10-6 30 x 10-6 – 60 x 10-6
Thermal conductivity perpendicular to cleavage plane Gm.cal/sec/cm2/°C/cm about 0.0013 about 0.0010
BTU/hr/ft2/0f/ft about 0.31 about 0.24
Thermal conductivity
parallel to cleavage plane		 Gm.cal/sec/cm2/°C/cm about 0.012
BTU/hr/ft2/0f/ft about 3.0
Water of Constitution % 4.5 3.0
Moisture Absorption Very low Very low
Volume Resistivity 25°C (77°F) ohm cm 40 x 1013 -2 x 1017 1 x 1012 -1 x 1012
Acid Reaction Affected by hydrofluoric acid affected by sulphuric acid
Insulation resistence x1013ohm/cm 4-20000 0.1 – 10
Calcining temp °C 700-800 900-1000
Max. operating temp °C 500-600 800-1000
Optic axial angle degrees 55 – 75 5 -25
Tensile strength MN/m2 175 1000
Shear strength MN/m2 220 – 270 1000-1300
Compression strength MN/m2 190 – 285 –
Modulus of Elasticity Kgfcm2 x 10-3lbf/in2 x 10-6 1400 – 210020 – 30 1400 – 2100 20 – 30
Loss tangent x10-4 1-4 10-50
Permittivity at 15°C (60°F) 6 – 7 5 -6