Muscovite mica
KAl2(AlSi3O10)(OH)2 · monoclinic
Muscovite mica is a hydrated potassium aluminium silicate with the formula KAl2(AlSi3O10)(OH)2 (Wikipedia).
Evidence level
2 of 5
Lab-measured
- 0Predicted only. No one has made it, or no measurement exists.
- 1Calculated. Only calculated or predicted values from sources.
- 2Lab-measured. Measured properties with their conditions stated.
- 3Space-relevant tests. Measured in conditions relevant to space, such as vacuum or atomic oxygen.
- 4Ground-qualified. Qualified for an application on the ground.
- 5Flown or field-proven. Flight or field results exist.
Dielectric constant
7.2
Power factor
0.02 per cent
Heat tolerance
500 degC continuous
Recipe, share of the weight
- K not statedPotassium
- Al not statedAluminium
- Si not statedSilicon
- O not statedOxygen
- H not statedHydrogen
Best for
Electrical insulation and capacitor dielectric where low dielectric loss and heat tolerance matter. NIST measured clear ruby muscovite at 0.02 per cent power factor.
Weakest at
Stained or inclusion-bearing mica. NIST found that stains and air bubbles raise the power factor so far that the mica is unsuited for radio purposes.
Risk at a glance
- People None found. Dust limits set by NIOSH and OSHA; no GHS data found
- If it fails Moderate. Stains or inclusions in the mica
- Corrosion Moderate. Most muscovite samples were practically unchanged after 30 minutes at 600 degC, but none withstood 1,200 degC well.
Quick facts: Muscovite mica
| Property | Value | Basis |
|---|---|---|
| Density | 2 to 2.35 g/cm³ | 1 sourced value |
| Tensile strength | 110 MPa | 1 sourced value |
| Thermal conductivity | 0.3 W/(m·K) | 1 sourced value |
| Maximum service temperature | 500 to 800 °C | 2 sourced values across conditions |
What is the density of Muscovite mica?
Muscovite mica has a density of 2 to 2.35 g/cm³. The source and test conditions are listed in the properties table on this page.
What is the thermal conductivity of Muscovite mica?
Muscovite mica has a thermal conductivity of 0.3 W/(m·K). The source and test conditions are listed in the properties table on this page.
What is the tensile strength of Muscovite mica?
Muscovite mica has a tensile strength of 110 MPa. The source and test conditions are listed in the properties table on this page.
What is the maximum service temperature of Muscovite mica?
Muscovite mica has a maximum service temperature of 500 to 800 °C. The range covers 2 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is Muscovite mica used for?
Uses recorded in the sources include Film capacitor dielectric; Electrical and electronic parts; Rigid mica sheet for thermal and electrical insulation.
Why it exists
Muscovite mica is a layered potassium aluminium silicate with the formula KAl2(AlSi3O10)(OH)2 (Wikipedia). It is the mica that electrical makers use most, and Wikipedia calls it the principal mica used by the electrical industry. NIST measured clear ruby muscovite at a dielectric constant of 7.2 and a power factor of 0.02 per cent at 25 degC, and those figures are the reference values in the 1931 study.
Where it's used
Capacitor dielectric
Wikipedia says only high-quality muscovite film mica, also called India ruby mica, is used as a dielectric in capacitors, and the highest grade is used in calibration-standard capacitors.
Electrical and electronic parts
USGS says that most sheet mica was made into parts for electrical and electronic equipment, and that the United States relied on imports for sheet mica.
High-temperature insulation
RS sells rigid mica sheet for thermal and electrical insulation, and lists a muscovite insulation film rated for 500 degC continuous and 800 degC intermittent.
Recipe
KAl2(AlSi3O10)(OH)2
Muscovite is a potassium aluminium silicate. Each formula unit, KAl2(AlSi3O10)(OH)2, holds one potassium atom, three aluminium atoms, three silicon atoms, twelve oxygen atoms and two hydrogen atoms, counted from the printed formula.
| Ingredient | Share of the weight | What it does |
|---|---|---|
| Potassium K | not stated | Sits between the silicate layers and balances the charge of the aluminium-silicate sheets. |
| Aluminium Al | not stated | Two aluminium atoms sit in the octahedral sites and one in a tetrahedral site of the layered structure (formula grouping (AlSi3O10)). |
| Silicon Si | not stated | Forms the silica tetrahedra of the layers with oxygen. |
| Oxygen O | not stated | Ten oxygens in the silicate framework and two in the hydroxyl groups. |
| Hydrogen H | not stated | Forms the two hydroxyl groups, (OH)2, in the printed formula. |
Weight shares are as printed in the sources.
What it can do
Dielectric constant
7.2
measured
NIST averaged 7.20 for 16 clear muscovite samples at 25 degC over 100 to 1,000 kilocycles, with individual samples varying by plus or minus 0.3.
Power factor
0.02 per cent
measured
NIST gives an average power factor of 0.02 per cent for the same clear muscovite, with individual samples varying by plus or minus 0.01 per cent.
Heat tolerance
500 degC continuous
measured
RS rates its muscovite insulation film at 500 degC continuous and 800 degC intermittent. NIST found that most muscovite was unchanged after 30 minutes at 600 degC.
How it compares
Muscovite mica is a low-loss, high-temperature dielectric. NIST measured its power factor at 0.02 per cent, and the RS datasheet rates the muscovite insulation film at 500 degC continuous. This profile holds mica values only, so it does not yet compare mica against other dielectrics. The compare table will fill in as the other dielectric profiles are written.
The same measurements for each material, so you can compare them. Each row names the key condition under the value; the full conditions and methods are in the numbered notes under Technical details.
| Measurement | Muscovite mica |
|---|---|
| Thermal behavior and safety | |
| Thermal conductivity, rigid mica sheet at 20 degC | 0.3 W/mK6 |
| Heat loss, rigid mica sheet at 500 degC | 1.5 %13 |
| Heat loss, rigid mica sheet at 700 degC | 2 %14 |
| Physical and electrical | |
| Density, rigid mica sheet | 2 g/cm³9 |
| Other measurements | |
| Dielectric constant, clear ruby muscovite | 7.2 -1 |
| Power factor (dissipation factor), clear ruby muscovite | 0.02 %2 |
| Dielectric strength, rigid mica sheet at 20 degC | 20 kV/mm3 |
| Dielectric strength, rigid mica sheet at 400 degC | 13 kV/mm4 |
| Dielectric strength, rigid mica sheet at 600 degC | 10 kV/mm5 |
| Maximum service temperature, muscovite insulation film, continuous | 500 °C7 |
| Maximum service temperature, muscovite insulation film, intermittent | 800 °C8 |
| Tensile strength, rigid mica sheet | 110 MPa10 |
| Flexural strength, rigid mica sheet | 80 MPa11 |
| Water absorption, rigid mica sheet | 0.5 %12 |
| Compressive strength perpendicular, rigid mica sheet | 200 MPa15 |
| Compressive strength parallel, rigid mica sheet | 50 MPa16 |
| Refractive index range, muscovite (three principal indices) | 1.552 -17 |
Why choose it, and why not
Good for
- Low power loss at radio frequencies. NIST measured 0.02 per cent power factor for clear ruby muscovite.
- High-temperature insulation. RS rates its muscovite insulation film at 500 degC continuous and 800 degC intermittent.
Watch out for
- Stained or bubbly mica. NIST found these raise the power factor too high for radio purposes.
- Temperatures above 600 degC. NIST found that muscovites kept their properties less well than phlogopites above that temperature, and none withstood 1,200 degC well.
- Species uncertainty in the RS sheet values. The RS sheet specifications are printed under the heading Muscovite Mica, but the stock item is named phlogopite, so confirm the species before design use.
Muscovite mica is a well-measured, low-loss insulator for electrical and capacitor use up to about 500 degC. Its loss is strongly affected by stains and bubbles, and the RS sheet values need their species confirmed.
Technical details
For scientists and researchers. Everything above comes from the record below: every number with its method, its conditions and its source.
Notes
The method, full conditions and any caveat for the numbered rows above.
| # | Measurement | Method | Conditions | Caveat |
|---|---|---|---|---|
| 1 | Dielectric constant, clear ruby muscovite | Average of measurements in NIST Table 1, row Clear muscovite | grade clear ruby muscovite, 16 samples from the United States and Indiafrequency 100 to 1,000 kilocycles (as printed)temperature 25 °Cspread +/-0.3 for individual samples (abstract) | — |
| 2 | Power factor (dissipation factor), clear ruby muscovite | NIST calls this property power factor; it is mapped to the dissipation-factor slot. Value printed as 0.02 per cent. | grade clear ruby muscovite, 16 samples from the United States and Indiafrequency 100 to 1,000 kilocycles (as printed)temperature 25 °Cunit in source per centspread +/-0.01 per cent for individual samples (abstract) | — |
| 3 | Dielectric strength, rigid mica sheet at 20 degC | Value printed in RS datasheet, Electrical Specifications table | temperature 20 °Cproduct RS PRO rigid mica sheet, printed under the heading Muscovite Mica (the stock item on page 1 is named phlogopite; see gaps) | — |
| 4 | Dielectric strength, rigid mica sheet at 400 degC | Value printed in RS datasheet, Electrical Specifications table | temperature 400 °Cproduct RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps) | — |
| 5 | Dielectric strength, rigid mica sheet at 600 degC | Value printed in RS datasheet, Electrical Specifications table | temperature 600 °Cproduct RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps) | — |
| 6 | Thermal conductivity, rigid mica sheet at 20 degC | Value printed in RS datasheet, Electrical Specifications table | temperature 20 °Cproduct RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)unit in source W/mK | — |
| 7 | Maximum service temperature, muscovite insulation film, continuous | Value printed in the Similar Products table of the RS datasheet | basis continuousproduct RS PRO Muscovite Mica Insulation Film, 0.2 mm, stock 785-0815 | — |
| 8 | Maximum service temperature, muscovite insulation film, intermittent | Value printed in the Similar Products table of the RS datasheet | basis intermittentproduct RS PRO Muscovite Mica Insulation Film, 0.2 mm, stock 785-0815 | — |
| 9 | Density, rigid mica sheet | Range printed in RS datasheet, General Specifications table | product RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)unit in source g/cm³ | — |
| 10 | Tensile strength, rigid mica sheet | Value printed in RS datasheet as N/mm²; N/mm² equals MPa | product RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)unit in source N/mm2 | — |
| 11 | Flexural strength, rigid mica sheet | Value printed in RS datasheet as N/mm²; N/mm² equals MPa | product RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)unit in source N/mm2test bending | — |
| 12 | Water absorption, rigid mica sheet | Maximum value printed as less than or equal to 0.5 per cent | basis maximum, 24 h at 23 °Cproduct RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps) | — |
| 13 | Heat loss, rigid mica sheet at 500 degC | Printed as less than 1.5 per cent; heat_loss is not a canonical property name | basis less thantemperature 500 °Cproduct RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps) | — |
| 14 | Heat loss, rigid mica sheet at 700 degC | Printed as less than 2 per cent; heat_loss is not a canonical property name | basis less thantemperature 700 °Cproduct RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps) | — |
| 15 | Compressive strength perpendicular, rigid mica sheet | Value printed as N/mm²; compressive_strength_perpendicular is not a canonical property name | direction perpendicularproduct RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)unit in source N/mm2 | — |
| 16 | Compressive strength parallel, rigid mica sheet | Value printed as N/mm²; compressive_strength_parallel is not a canonical property name | direction parallelproduct RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)unit in source N/mm2 | — |
| 17 | Refractive index range, muscovite (three principal indices) | Lowest (1.552) and highest (1.618) of the printed principal refractive indices. The PDF text layer drops the Greek letter labels, so the values are not tied to a single optical axis. | basis lowest and highest of the three principal indices printed | — |
Corrosion and compatibility
What happens when it meets other materials and environments.
| Environment | Concern | What happens |
|---|---|---|
| Furnace heating for 30 minutes at 600 degC | moderate | Most muscovite samples were practically unchanged after 30 minutes at 600 degC, but none withstood 1,200 degC well.1 |
| Water exposure, 24 h at 23 degC | low | The RS mica sheet absorbs at most 0.5 per cent water in 24 hours.2 |
| Heat loss at 500 degC and 700 degC | moderate | The RS mica sheet shows heat loss of less than 1.5 per cent at 500 degC and less than 2 per cent at 700 degC.3 |
| # | Environment | Details | Test conditions |
|---|---|---|---|
| 1 | Furnace heating for 30 minutes at 600 degC | NIST heated 1 by 2.5 cm samples for one-half hour at temperatures from 600 degC to 1,200 degC. With one or two exceptions the micas were unaffected by 600 degC. Above 600 degC the phlogopites kept their properties better than the muscovites. | exposure one-half hour at each temperature, rapid heating, no external forcetest furnace, samples graded for colour, surface, opacity, lamina separation and form |
| 2 | Water exposure, 24 h at 23 degC | Printed as less than or equal to 0.5 per cent. RS also lists the product as moisture resistant on page 1 of the datasheet. | basis 24 h at 23 °Cproduct RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps) |
| 3 | Heat loss at 500 degC and 700 degC | The datasheet prints these heat loss figures without a test duration. The same sheet has a continuous heat-resistance rating of 600 degC on page 2. | product RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps) |
Risks and side effects
Hazards to people, what happens when a cell overheats, and how the material is handled and stored.
For people
NIOSH and OSHA list mica (containing less than 1% quartz) with muscovite as a synonym. Neither page prints a GHS classification, and no safety data sheet for muscovite itself was found, so this profile cannot rate the powder beyond its dust limits.
- The powder
- Keep dust below the respirable limit that NIOSH and OSHA set for mica, and check the supplier's safety data sheet for the grade you handle before cutting or grinding.
Test details
The original wording and numbers from the sources, for readers who want them.
Failure risks
| Failure | Trigger and consequence |
|---|---|
| Stains or inclusions in the micamoderate severity | Air bubbles or metallic-oxide stains in the sheetNIST found that the slightest trace of air bubbles or metallic oxides raises the power factor so far that the mica is unsuited for applications needing low power loss, although dielectric strength is much less affected. |
| Exposure above 600 degCmoderate severity | Heating muscovite above 600 degC for 30 minutes (the NIST test condition)NIST found that above 600 degC the phlogopites kept their properties better than the muscovites, and that none of the micas tested withstands 1,200 degC well. |
Handling and storage
- The RS mica sheet is listed as easy to cut or punch and moisture resistant (page 1 features list). The page-1 stock item is named phlogopite, so confirm the species on the supplier's sheet.
- Keep stains and air bubbles out of capacitor-grade sheet, because NIST found that stained or bubbled mica has a much higher power factor.
Mitigations
- Select clear, unstained sheet for radio and low-loss uses. NIST found that stained micas are unsuited for radio purposes.
Supply and geography
How common the raw materials are and where they come from.
Mica (natural), sheet and scrap or flake
Not found in the sources read for this profile.
- Top producers (2025)
- China, Madagascar, Finland, India
- Recycling
- None (USGS Salient Statistics: Recycling: None).
- Substitutes
- Mica paper made from scrap mica can be substituted for sheet mica in electrical and insulation applications (USGS).; Ground synthetic fluorophlogopite may replace natural ground mica for uses that require the thermal and electrical properties of mica (USGS).; Acrylic, cellulose acetate, fiberglass, fishpaper, nylon, phenolics, polycarbonate, polyester, polyvinyl chloride and vulcanized fiber can be substituted for mica in many electrical, electronic and insulation uses (USGS).
Documents
Datasheets, safety data sheets, papers and standards you can open.
Full record
The complete spore, as stored. Free to reuse under CC-BY-4.0. Images keep the licence shown with each one.
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spore: profile
id: mica-muscovite
spore_version: 0.2
family: mica
name: Muscovite mica
role: dielectric
category: electronics
type: dielectrics-and-capacitors
summary: |
Muscovite mica is a hydrated potassium aluminium silicate with the formula KAl2(AlSi3O10)(OH)2 (Wikipedia). In a 1931 National Bureau of Standards study, clear ruby muscovite averaged a dielectric constant of 7.2 and a power factor of 0.02 per cent at 25 degC over 100 to 1,000 kilocycles. A rigid mica sheet datasheet from RS PRO gives a dielectric strength of 20 kV/mm at 20 degC, and an RS muscovite insulation film is rated for 500 degC continuous service.
best_for: Electrical insulation and capacitor dielectric where low dielectric loss and heat tolerance matter. NIST measured clear ruby muscovite at 0.02 per cent power factor.
weakest_at: Stained or inclusion-bearing mica. NIST found that stains and air bubbles raise the power factor so far that the mica is unsuited for radio purposes.
identity:
formula: KAl2(AlSi3O10)(OH)2
crystal_system: monoclinic
source: wiki-muscovite
where: Opening text and infobox (formula and crystal system)
tags:
environments: []
stresses: []
applications:
- electronics-and-chips
- thermal-control
properties:
- benchmark: dielectric_constant
label: Dielectric constant, clear ruby muscovite
value: 7.2
unit: '-'
scope: material
conditions:
grade: clear ruby muscovite, 16 samples from the United States and India
frequency: 100 to 1,000 kilocycles (as printed)
temperature: 25 degC
spread: +/-0.3 for individual samples (abstract)
method: Average of measurements in NIST Table 1, row Clear muscovite
status: ground
source: nist-rp347
where: Abstract; Table 1, row 'Clear muscovite' (16 samples, average 7.20)
- benchmark: dissipation_factor
label: Power factor (dissipation factor), clear ruby muscovite
value: 0.02
unit: '%'
scope: material
conditions:
grade: clear ruby muscovite, 16 samples from the United States and India
frequency: 100 to 1,000 kilocycles (as printed)
temperature: 25 degC
unit_in_source: per cent
spread: +/-0.01 per cent for individual samples (abstract)
method: NIST calls this property power factor; it is mapped to the dissipation-factor slot. Value printed as 0.02 per cent.
status: ground
source: nist-rp347
where: Abstract; Table 1, row 'Clear muscovite' (average 0.02 per cent)
- benchmark: dielectric_strength
label: Dielectric strength, rigid mica sheet at 20 degC
value: 20
unit: kV/mm
scope: material
conditions:
temperature: 20 degC
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (the stock item on page 1 is named phlogopite; see gaps)
method: Value printed in RS datasheet, Electrical Specifications table
status: ground
source: rs-mica
where: Page 3, Electrical Specifications, Dielectric Strength 20 C row
- benchmark: dielectric_strength
label: Dielectric strength, rigid mica sheet at 400 degC
value: 13
unit: kV/mm
scope: material
conditions:
temperature: 400 degC
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
method: Value printed in RS datasheet, Electrical Specifications table
status: ground
source: rs-mica
where: Page 3, Electrical Specifications, Dielectric Strength 400 C row
- benchmark: dielectric_strength
label: Dielectric strength, rigid mica sheet at 600 degC
value: 10
unit: kV/mm
scope: material
conditions:
temperature: 600 degC
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
method: Value printed in RS datasheet, Electrical Specifications table
status: ground
source: rs-mica
where: Page 3, Electrical Specifications, Dielectric Strength 600 C row
- benchmark: thermal_conductivity
label: Thermal conductivity, rigid mica sheet at 20 degC
value: 0.3
unit: W/mK
scope: material
conditions:
temperature: 20 degC
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
unit_in_source: W/mK
method: Value printed in RS datasheet, Electrical Specifications table
status: ground
source: rs-mica
where: Page 3, Electrical Specifications, Thermal Conductivity (20 C) row
- benchmark: max_service_temp
label: Maximum service temperature, muscovite insulation film, continuous
value: 500
unit: °C
scope: material
conditions:
basis: continuous
product: RS PRO Muscovite Mica Insulation Film, 0.2 mm, stock 785-0815
method: Value printed in the Similar Products table of the RS datasheet
status: ground
source: rs-mica
where: Page 3, Similar Products table, row 785-0815 (Max Temp column)
- benchmark: max_service_temp
label: Maximum service temperature, muscovite insulation film, intermittent
value: 800
unit: °C
scope: material
conditions:
basis: intermittent
product: RS PRO Muscovite Mica Insulation Film, 0.2 mm, stock 785-0815
method: Value printed in the Similar Products table of the RS datasheet
status: ground
source: rs-mica
where: Page 3, Similar Products table, row 785-0815 (Max Temp column)
- benchmark: density
label: Density, rigid mica sheet
value: 2
value_high: 2.35
unit: g/cm3
scope: material
conditions:
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
unit_in_source: g/cm³
method: Range printed in RS datasheet, General Specifications table
status: ground
source: rs-mica
where: Page 2, General Specifications, Density row
- benchmark: ultimate_tensile_strength
label: Tensile strength, rigid mica sheet
value: 110
unit: MPa
scope: material
conditions:
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
unit_in_source: N/mm2
method: Value printed in RS datasheet as N/mm²; N/mm² equals MPa
status: ground
source: rs-mica
where: Page 2, Mechanical Specifications, Tensile Strength row
- benchmark: flexural_strength
label: Flexural strength, rigid mica sheet
value: 80
unit: MPa
scope: material
conditions:
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
unit_in_source: N/mm2
test: bending
method: Value printed in RS datasheet as N/mm²; N/mm² equals MPa
status: ground
source: rs-mica
where: Page 2, Mechanical Specifications, Flexural Strength (Bending) row
- benchmark: moisture_absorption
label: Water absorption, rigid mica sheet
value: 0.5
unit: '%'
scope: material
conditions:
basis: maximum, 24 h at 23 degC
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
method: Maximum value printed as less than or equal to 0.5 per cent
status: ground
source: rs-mica
where: Page 2, Mechanical Specifications, Water Absorption row
- benchmark: heat_loss
label: Heat loss, rigid mica sheet at 500 degC
value: 1.5
unit: '%'
scope: material
conditions:
basis: less than
temperature: 500 degC
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
method: Printed as less than 1.5 per cent; heat_loss is not a canonical property name
status: ground
source: rs-mica
where: Page 3, Electrical Specifications, Heat Loss 500 C row
- benchmark: heat_loss
label: Heat loss, rigid mica sheet at 700 degC
value: 2
unit: '%'
scope: material
conditions:
basis: less than
temperature: 700 degC
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
method: Printed as less than 2 per cent; heat_loss is not a canonical property name
status: ground
source: rs-mica
where: Page 3, Electrical Specifications, Heat Loss 700 C row
- benchmark: compressive_strength_perpendicular
label: Compressive strength perpendicular, rigid mica sheet
value: 200
unit: MPa
scope: material
conditions:
direction: perpendicular
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
unit_in_source: N/mm2
method: Value printed as N/mm²; compressive_strength_perpendicular is not a canonical property name
status: ground
source: rs-mica
where: Page 2, Mechanical Specifications, Compressive Strength, Perpendicular row
- benchmark: compressive_strength_parallel
label: Compressive strength parallel, rigid mica sheet
value: 50
unit: MPa
scope: material
conditions:
direction: parallel
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
unit_in_source: N/mm2
method: Value printed as N/mm²; compressive_strength_parallel is not a canonical property name
status: ground
source: rs-mica
where: Page 2, Mechanical Specifications, Compressive Strength, Parallel row
- benchmark: refractive_index
label: Refractive index range, muscovite (three principal indices)
value: 1.552
value_high: 1.618
unit: '-'
scope: material
conditions:
basis: lowest and highest of the three principal indices printed
method: Lowest (1.552) and highest (1.618) of the printed principal refractive indices. The PDF text layer drops the Greek letter labels, so the values are not tied to a single optical axis.
status: ground
source: handbook-muscovite
where: Optical Properties paragraph (refractive index values 1.552 to 1.576, 1.582 to 1.615 and 1.587 to 1.618)
corrosion:
- environment: Furnace heating for 30 minutes at 600 degC
headline: Most muscovite samples were practically unchanged after 30 minutes at 600 degC, but none withstood 1,200 degC well.
effect: NIST heated 1 by 2.5 cm samples for one-half hour at temperatures from 600 degC to 1,200 degC. With one or two exceptions the micas were unaffected by 600 degC. Above 600 degC the phlogopites kept their properties better than the muscovites.
rating: moderate
conditions:
exposure: one-half hour at each temperature, rapid heating, no external force
test: furnace, samples graded for colour, surface, opacity, lamina separation and form
source: nist-rp347
where: Abstract; Section 4 (Effects of elevated temperatures); Conclusions
- environment: Water exposure, 24 h at 23 degC
headline: The RS mica sheet absorbs at most 0.5 per cent water in 24 hours.
effect: Printed as less than or equal to 0.5 per cent. RS also lists the product as moisture resistant on page 1 of the datasheet.
rating: low
conditions:
basis: 24 h at 23 degC
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
source: rs-mica
where: Page 2, Mechanical Specifications, Water Absorption row; page 1, Features list
- environment: Heat loss at 500 degC and 700 degC
headline: The RS mica sheet shows heat loss of less than 1.5 per cent at 500 degC and less than 2 per cent at 700 degC.
effect: The datasheet prints these heat loss figures without a test duration. The same sheet has a continuous heat-resistance rating of 600 degC on page 2.
rating: moderate
conditions:
product: RS PRO rigid mica sheet, printed under the heading Muscovite Mica (species uncertain; see gaps)
source: rs-mica
where: Page 3, Electrical Specifications, Heat Loss rows (500 C and 700 C)
uses:
- application: electronics-and-chips
device: Film capacitor dielectric
example: Wikipedia states that only high-quality muscovite film mica, also called India ruby mica, is used as a dielectric in capacitors, and that the highest-grade film is used in calibration-standard capacitors.
source: wiki-mica
where: Section on electrical insulation and capacitors
- application: electronics-and-chips
device: Electrical and electronic parts
example: USGS reports that most sheet mica was fabricated into parts for electrical and electronic equipment, and that the United States depended on imports to meet demand for sheet mica.
source: usgs-mcs2026-mica
where: Domestic Production and Use paragraph (2025)
- application: thermal-control
device: Rigid mica sheet for thermal and electrical insulation
example: RS describes its rigid mica sheets as providing outstanding thermal and electrical insulation in a broad range of industries, with a low thermal conductivity and high dielectric strength.
source: rs-mica
where: Page 2, Product Description
risks:
hazards:
- text: NIOSH lists mica (containing less than 1% quartz), with muscovite among its synonyms, at a recommended exposure limit of TWA 3 mg/m3 (resp), an IDLH of 1500 mg/m3 and a target organ of the respiratory system. Symptoms listed include irritation of the eyes, pneumoconiosis, cough and dyspnea (breathing difficulty). Exposure routes listed are inhalation, skin and/or eye contact.
ghs: []
source: niosh-mica
where: Synonyms and Trade Names; Exposure Limits; IDLH; symptom and target organ entries
- text: OSHA lists mica (CAS 12001-26-2) with an 8-hour TWA of 20 mppcf for respirable dust, and no STEL or ceiling. The OSHA page prints no health-effects text and refers readers to PubChem for health factors.
ghs: []
source: osha-mica
where: Permissible exposure limits section; health factors line
failure_risks:
- mode: Stains or inclusions in the mica
trigger: Air bubbles or metallic-oxide stains in the sheet
consequence: NIST found that the slightest trace of air bubbles or metallic oxides raises the power factor so far that the mica is unsuited for applications needing low power loss, although dielectric strength is much less affected.
severity: moderate
source: nist-rp347
where: Abstract; Section IV (Discussion and conclusions)
- mode: Exposure above 600 degC
trigger: Heating muscovite above 600 degC for 30 minutes (the NIST test condition)
consequence: NIST found that above 600 degC the phlogopites kept their properties better than the muscovites, and that none of the micas tested withstands 1,200 degC well.
severity: moderate
source: nist-rp347
where: Abstract; Section IV (Discussion and conclusions)
side_effects: []
handling:
- text: The RS mica sheet is listed as easy to cut or punch and moisture resistant (page 1 features list). The page-1 stock item is named phlogopite, so confirm the species on the supplier's sheet.
source: rs-mica
where: Page 1, Features list
- text: Keep stains and air bubbles out of capacitor-grade sheet, because NIST found that stained or bubbled mica has a much higher power factor.
source: nist-rp347
where: Abstract; Section IV (Discussion and conclusions)
mitigations:
- text: Select clear, unstained sheet for radio and low-loss uses. NIST found that stained micas are unsuited for radio purposes.
source: nist-rp347
where: Abstract
supply:
- subject: Mica (natural), sheet and scrap or flake
abundance: Not found in the sources read for this profile.
producers:
- country: China
tonnes: 85,000 (scrap and flake mine production, 2025 estimate)
reserves: 1,100,000 (scrap and flake); 75,000 (sheet)
year: 2025
- country: Madagascar
tonnes: 70,000 (scrap and flake mine production, 2025)
year: 2025
- country: Finland
tonnes: 57,000 (scrap and flake mine production, 2025)
year: 2025
- country: India
tonnes: 1,000 (sheet mine production, 2025)
reserves: 110,000 (sheet)
year: 2025
critical_lists: []
recycling: 'None (USGS Salient Statistics: Recycling: None).'
substitutes:
- Mica paper made from scrap mica can be substituted for sheet mica in electrical and insulation applications (USGS).
- Ground synthetic fluorophlogopite may replace natural ground mica for uses that require the thermal and electrical properties of mica (USGS).
- Acrylic, cellulose acetate, fiberglass, fishpaper, nylon, phenolics, polycarbonate, polyester, polyvinyl chloride and vulcanized fiber can be substituted for mica in many electrical, electronic and insulation uses (USGS).
source: usgs-mcs2026-mica
where: World Mine Production and Reserves table; Substitutes paragraph; Salient Statistics table (sheet imports and import reliance)
documents:
- title: Some Electrical Properties of Foreign and Domestic Micas and the Effect of Elevated Temperatures (NBS Research Paper RP347), A. B. Lewis, E. L. Hall and F. R. Caldwell
type: paper
url: https://nvlpubs.nist.gov/nistpubs/jres/7/jresv7n2p403_A2b.pdf
year: 1931
- title: RS PRO rigid mica sheet and muscovite mica insulation film datasheet (stock 134-940 and 785-0815)
type: datasheet
url: https://docs.rs-online.com/0045/A700000015993317.pdf
- title: 'USGS Mineral Commodity Summaries 2026: Mica (Natural)'
type: report
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-mica.pdf
year: 2026
- title: 'Handbook of Mineralogy: Muscovite (Mineral Data Publishing, version 1.2)'
type: report
url: https://www.handbookofmineralogy.org/pdfs/muscovite.pdf
year: 2001
- title: 'NIOSH Pocket Guide to Chemical Hazards: Mica (containing less than 1% quartz)'
type: database
url: https://www.cdc.gov/niosh/npg/npgd0431.html
- title: 'OSHA Chemical Data: Mica (CAS 12001-26-2)'
type: database
url: https://www.osha.gov/chemicaldata/153
gaps:
- No safety data sheet, GHS classification or PubChem record for muscovite itself was found. PubChem returned a browser-check page. The hazards entries use the NIOSH and OSHA mica entries, which cover mica containing less than 1% quartz and list muscovite as a synonym. Neither gives GHS data.
- CAS number, UNS, EN, ASTM and other designations for muscovite were not printed in any source used, so identity.designations is left out. NIOSH and OSHA print CAS 12001-26-2 for the mica group, which lists muscovite as a synonym; it is not entered as a muscovite-specific designation.
- Space group and atomic weights were not printed in the sources read, so they are left out.
- Density is printed without a unit in both the Handbook of Mineralogy (D(meas.) 2.77 to 2.88; D(calc.) 2.83) and Wikipedia (specific gravity 2.76 to 3), so no density value was entered from those pages. Mohs hardness (Handbook 2.5; Wikipedia 2 to 2.25 or 2 to 2.5) is on an ordinal scale and was not entered. The Handbook refractive indices are entered, but the PDF text layer drops their Greek labels, so they are not tied to an optical axis.
- The RS datasheet prints its specification tables under the heading Muscovite Mica, but the page-1 stock item 134-940 is named RS PRO Phlogopite Mica. The species of the rigid-sheet values (dielectric strength, density, tensile, flexural, compressive, water absorption, thermal conductivity, heat loss) is therefore uncertain and should be confirmed with the supplier.
- Volume resistivity was printed by RS as 1016 and 109 ohm/cm (superscripts lost in text extraction), so those values were not entered.
- Compressive strength and heat loss use names that are not in spores/property-canon.yaml (compressive_strength_perpendicular, compressive_strength_parallel, heat_loss).
- NIST Table 2 gives clear ruby muscovite breakdown voltages of 5.7, 9.9 and 13.2 kilovolts (effective) at 1, 5 and 9 mils, which is total breakdown voltage and not kV/mm, so it is not entered as dielectric strength. The NIST values appear in the story text.
- No vacuum, outgassing, radiation or space-flight data for muscovite mica were found in the sources read.
- The Wikipedia values were read through a summarising fetch. The mica-group statement that mica is thermally stable to 500 degC is general to mica and is not muscovite-specific, so it is used only in the story text.
- Abundance in the crust, critical-mineral list status and production shares by percentage were not found in the USGS page read.
- No images were added.
sources:
nist-rp347:
title: Some Electrical Properties of Foreign and Domestic Micas and the Effect of Elevated Temperatures (NBS Research Paper RP347), A. B. Lewis, E. L. Hall and F. R. Caldwell
url: https://nvlpubs.nist.gov/nistpubs/jres/7/jresv7n2p403_A2b.pdf
year: 1931
kind: paper
rs-mica:
title: RS PRO rigid mica sheet and muscovite mica insulation film datasheet (stock 134-940 and 785-0815)
url: https://docs.rs-online.com/0045/A700000015993317.pdf
kind: datasheet
usgs-mcs2026-mica:
title: 'USGS Mineral Commodity Summaries 2026: Mica (Natural)'
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-mica.pdf
year: 2026
kind: report
wiki-mica:
title: 'Wikipedia: Mica'
url: https://en.wikipedia.org/wiki/Mica
kind: web
wiki-muscovite:
title: 'Wikipedia: Muscovite'
url: https://en.wikipedia.org/wiki/Muscovite
kind: web
handbook-muscovite:
title: 'Handbook of Mineralogy: Muscovite (Mineral Data Publishing, version 1.2)'
url: https://www.handbookofmineralogy.org/pdfs/muscovite.pdf
year: 2001
kind: handbook
niosh-mica:
title: 'NIOSH Pocket Guide to Chemical Hazards: Mica (containing less than 1% quartz)'
url: https://www.cdc.gov/niosh/npg/npgd0431.html
kind: handbook
osha-mica:
title: 'OSHA Chemical Data: Mica (CAS 12001-26-2)'
url: https://www.osha.gov/chemicaldata/153
kind: database
license: CC-BY-4.0
updated: '2026-11-01'
review:
status: draft
method: assistant
checked_values: 17
note: Written by an AI assistant on 2026-11-01 from the eight sources listed, using only numbers printed in those sources. Hazard entries use the NIOSH and OSHA mica entries, which list muscovite as a synonym.
story:
recipe:
line: Muscovite is a potassium aluminium silicate. Each formula unit, KAl2(AlSi3O10)(OH)2, holds one potassium atom, three aluminium atoms, three silicon atoms, twelve oxygen atoms and two hydrogen atoms, counted from the printed formula.
parts:
- name: Potassium
symbol: K
role: Sits between the silicate layers and balances the charge of the aluminium-silicate sheets.
- name: Aluminium
symbol: Al
role: Two aluminium atoms sit in the octahedral sites and one in a tetrahedral site of the layered structure (formula grouping (AlSi3O10)).
- name: Silicon
symbol: Si
role: Forms the silica tetrahedra of the layers with oxygen.
- name: Oxygen
symbol: O
role: Ten oxygens in the silicate framework and two in the hydroxyl groups.
- name: Hydrogen
symbol: H
role: Forms the two hydroxyl groups, (OH)2, in the printed formula.
risk_groups:
- title: For people
level: 0
verdict: Dust limits set by NIOSH and OSHA; no GHS data found
lead: NIOSH and OSHA list mica (containing less than 1% quartz) with muscovite as a synonym. Neither page prints a GHS classification, and no safety data sheet for muscovite itself was found, so this profile cannot rate the powder beyond its dust limits.
points:
- label: The powder
line: Keep dust below the respirable limit that NIOSH and OSHA set for mica, and check the supplier's safety data sheet for the grade you handle before cutting or grinding.
why: Muscovite mica is a layered potassium aluminium silicate with the formula KAl2(AlSi3O10)(OH)2 (Wikipedia). It is the mica that electrical makers use most, and Wikipedia calls it the principal mica used by the electrical industry. NIST measured clear ruby muscovite at a dielectric constant of 7.2 and a power factor of 0.02 per cent at 25 degC, and those figures are the reference values in the 1931 study.
uses:
- where: Capacitor dielectric
line: Wikipedia says only high-quality muscovite film mica, also called India ruby mica, is used as a dielectric in capacitors, and the highest grade is used in calibration-standard capacitors.
- where: Electrical and electronic parts
line: USGS says that most sheet mica was made into parts for electrical and electronic equipment, and that the United States relied on imports for sheet mica.
- where: High-temperature insulation
line: RS sells rigid mica sheet for thermal and electrical insulation, and lists a muscovite insulation film rated for 500 degC continuous and 800 degC intermittent.
can_do:
- label: Dielectric constant
benchmark: dielectric_constant
value: '7.2'
line: NIST averaged 7.20 for 16 clear muscovite samples at 25 degC over 100 to 1,000 kilocycles, with individual samples varying by plus or minus 0.3.
- label: Power factor
benchmark: dissipation_factor
value: 0.02 per cent
line: NIST gives an average power factor of 0.02 per cent for the same clear muscovite, with individual samples varying by plus or minus 0.01 per cent.
- label: Heat tolerance
benchmark: max_service_temp
value: 500 degC continuous
line: RS rates its muscovite insulation film at 500 degC continuous and 800 degC intermittent. NIST found that most muscovite was unchanged after 30 minutes at 600 degC.
compare: Muscovite mica is a low-loss, high-temperature dielectric. NIST measured its power factor at 0.02 per cent, and the RS datasheet rates the muscovite insulation film at 500 degC continuous. This profile holds mica values only, so it does not yet compare mica against other dielectrics. The compare table will fill in as the other dielectric profiles are written.
compare_rows:
- label: Dielectric constant
benchmark: dielectric_constant
- label: Power factor (dissipation factor)
benchmark: dissipation_factor
- label: Maximum service temperature
benchmark: max_service_temp
handling:
- Keep the sheet free of stains and air bubbles if it is used for low-loss or radio work, because NIST found these raise the power factor.
- Cut or punch the sheet as needed, since RS lists the rigid sheet as easy to cut or punch.
- Keep dust below the respirable limit that NIOSH and OSHA set for mica, and check the supplier's safety data sheet for the grade you handle.
good_for:
- Low power loss at radio frequencies. NIST measured 0.02 per cent power factor for clear ruby muscovite.
- High-temperature insulation. RS rates its muscovite insulation film at 500 degC continuous and 800 degC intermittent.
watch_out:
- Stained or bubbly mica. NIST found these raise the power factor too high for radio purposes.
- Temperatures above 600 degC. NIST found that muscovites kept their properties less well than phlogopites above that temperature, and none withstood 1,200 degC well.
- Species uncertainty in the RS sheet values. The RS sheet specifications are printed under the heading Muscovite Mica, but the stock item is named phlogopite, so confirm the species before design use.
verdict: Muscovite mica is a well-measured, low-loss insulator for electrical and capacitor use up to about 500 degC. Its loss is strongly affected by stains and bubbles, and the RS sheet values need their species confirmed.
References
Every number above carries a reference number. Click one to see the source and where in it the value comes from.
| # | Source | Type | Year | Used for |
|---|---|---|---|---|
| Some Electrical Properties of Foreign and Domestic Micas and the Effect of Elevated Temperatures (NBS Research Paper RP347), A. B. Lewis, E. L. Hall and F. R. Caldwell | paper | 1931 | 7 values | |
| RS PRO rigid mica sheet and muscovite mica insulation film datasheet (stock 134-940 and 785-0815) | datasheet | 18 values | ||
| USGS Mineral Commodity Summaries 2026: Mica (Natural) | report | 2026 | 2 values | |
| Wikipedia: Mica | web | 1 value | ||
| Wikipedia: Muscovite | web | 1 value | ||
| Handbook of Mineralogy: Muscovite (Mineral Data Publishing, version 1.2) | handbook | 2001 | 1 value | |
| NIOSH Pocket Guide to Chemical Hazards: Mica (containing less than 1% quartz) | handbook | 1 value | ||
| OSHA Chemical Data: Mica (CAS 12001-26-2) | database | 1 value |
Updated