Steatite
ASTM C773 L-5 · ISO IEC 60672 Type C-221 · also Magnesium Silicate
Steatite is a magnesium-silicate silicate ceramic made from a talc–clay–flux batch and fired to a dense, low-dielectric-loss body, supplied to ASTM C773 L-5 in as-fired, C-221 and porous grades.
Reference datasheet — Steatite is not in the instant-quote catalog. Upload your part and an engineer will quote it in this grade or suggest the closest stocked equivalent.
Values for the As Fired condition
Steatite tempers and conditions
Steatite is supplied in 3 conditions, soft to hard. As Fired is the default FabDigit quotes; the values on this page are for it.
Compare all 3 conditionsHide
| Condition · open for datasheet | Best for | Yield MPa | Tensile MPa | Elong. % | Hardness | Conductivity |
|---|---|---|---|---|---|---|
Porous steatite | Pick for wire-wound resistor cores, bobbins and burner parts where open porosity aids cement bonding and thermal-shock survival, and strength is secondary. | 20 | 400 HV | 1 W/m·K | ||
As FiredDefault dense vitrified steatite (ASTM D116 C-220) | Standard dense, zero-porosity steatite as fired — general-purpose low-cost HF insulator and heater/terminal component. | 60 | 650 HV | 3 W/m·K | ||
Low-loss steatite | Pick when RF/VHF loss matters: alkali content is minimised so the 1 MHz loss tangent is roughly half that of C-220. | 680 HV | 3 W/m·K |
What is Steatite?
Steatite is a magnesium-silicate silicate ceramic made from a talc–clay–flux batch and fired to a dense, low-dielectric-loss body, supplied to ASTM C773 L-5 in as-fired, C-221 and porous grades. Engineers use it as a low-cost electrical and mechanical insulator at 2.8 g/cm³, 60 MPa tensile strength, 100 GPa modulus, 2.5 W/m·K and 1000 °C service, in dry-pressed and extruded shapes such as insulators, bushings and coil supports. Fired parts machine poorly (score 8) and need diamond work, so dimensions are set in the green state ahead of 10–14 % firing shrinkage. Alumina is the step up when higher strength or temperature is required. Steatite has a density of 2.8 g/cm³ (0.101 lb/in³), lighter than 80% of ceramic grades. It melts at 1,450°C (2,642 °F). Steatite has a tensile strength of 60 MPa (8.7 ksi), weaker than 63% of ceramic grades. Elongation at break is 0% and the elastic modulus is 100 GPa (14.5 Msi).
What is Steatite used for?
- Electrical insulators and bushings
- Heater coil supports
- Terminal blocks and fuse bodies
- Thermostat and switch insulating parts
- Lamp holders and sockets
- Extruded insulating tubes and beads
- Gas burner insulators
Advantages
- Low embodied carbon — 1.9 kg CO₂/kg, better than 94% of ceramic grades
- Lightweight — 2.8 g/cm³ (0.101 lb/in³), better than 80% of ceramic grades
Limitations
- Poor heat conductor — 2.5 W/m·K (1.44 BTU/hr·ft·°F), worse than 83% of ceramic grades
- Hard to polish — 60/100, worse than 79% of ceramic grades
Steatite properties
Typical room-temperature values for Steatite-As Fired; bars are the position among ceramic grades.
Physical3
Steatite has a density of 2.8 g/cm³ (0.101 lb/in³), lighter than 80% of ceramic grades. It melts at 1,450°C (2,642 °F).
Mechanical12
Steatite has a tensile strength of 60 MPa (8.7 ksi), weaker than 63% of ceramic grades. Elongation at break is 0% and the elastic modulus is 100 GPa (14.5 Msi).
Thermal5
Steatite is rated for continuous service to 1,000°C (1,832 °F). It conducts heat at 2.5 W/m·K (1.44 BTU/hr·ft·°F), worse than 83% of ceramic grades. Thermal expansion is 8 µm/m·K (4.44 µin/in·°F).
Electrical5
Steatite is an electrical insulator with a dielectric strength of 12 kV/mm (304.8 V/mil) and a resistivity of 1×10¹² Ω·m.
Chemical & Environmental2
Corrosion resistance is excellent (85/100), better than 69% of ceramic grades.
Sustainability4
Producing a kilogram of Steatite takes about 27 MJ of energy and emits 1.9 kg of CO₂ — less than 95% of ceramic grades. Typical recycled content is 2%.
Manufacturability3
Steatite's machinability is not recommended (8/100, better than 69% of ceramic grades).
Common Calculations4
Values are nominal handbook figures for design screening. Certified mill or lot data ships with every FabDigit order on request.
Strength versus weight in the ceramic family
Yield strength against density for every ceramic grade FabDigit runs. Steatite is highlighted; hover a dot for its name, or open the interactive family chart.
Working with Steatite
Is Steatite easy to machine?
Machine in the green/bisque state (drill, turn, mill dry with carbide) allowing ~10–14 % firing shrinkage; fired parts require diamond grinding, lapping or laser/ultrasonic drilling.
Can Steatite be welded?
Not weldable — join by glass frit, ceramic cement, active-metal or Mo-Mn metallizing plus brazing, or mechanical clamping with compliant gaskets.
Can Steatite be formed, bent or molded?
Dry-pressed, isostatically pressed, extruded (tubes/rods) or injection/wet-pressed from talc–clay–flux batches, then fired at 1250–1350 °C; the vitrification window is narrow (~±20 °C), so temperature uniformity controls warpage and porosity.
Steatite chemical composition (wt %)
Limits by weight percent from the governing specification, written the way the spec states them — a single maximum for impurities, a range for alloying elements, and the base element as balance. Nominal is the typical mid-range value.
| Element | Spec limit (wt %) | Nominal |
|---|---|---|
| SiO2from talc + clay | 55 – 65 | 61 |
| MgOprotoenstatite former | 25 – 32 | 29 |
| Al2O3clay addition | 2 – 8 | 5 |
| BaOflux; BaCO3 used in low-loss C-221 instead of alkali feldspar | 0 – 6 | 3 |
| CaO | 0 – 2 | 0.7 |
| Na2O+K2Okept <0.5 % in low-loss C-221 | 0 – 2 | 0.5 |
| Fe2O3impurity | 0 – 1 | 0.3 |
What surface finishes work on Steatite?
Fired surface is naturally smooth and can be glazed for tracking resistance; ground/lapped for flatness, and Mo-Mn or thick-film Ag metallizing is used for solderable/brazable pads.
Equivalent designations
Standards and trade names that resolve to Steatite in FabDigit's catalog. Equivalence is nominal — check the exact specification when certification matters.
- ASTM
- C773 L-5
- ISO
- IEC 60672 Type C-221
- Trade names
- Magnesium Silicate
- Other
- 60672-3 C221
How much does Steatite cost?
Steatite is a high-cost ceramic ($$$$), pricier than about 98% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Steatite — frequently asked
What is Steatite used for?
Steatite is typically used for electrical insulators and bushings, heater coil supports, terminal blocks and fuse bodies, thermostat and switch insulating parts, lamp holders and sockets and extruded insulating tubes and beads. In short: low-cost electrical porcelain.
What is the tensile strength of Steatite?
Steatite has a typical tensile strength of 60 MPa (8.7 ksi) — weaker than 63% of ceramic grades. Strength varies by condition: see the 3 listed tempers.
Is Steatite easy to machine?
Not especially — machinability is rated not recommended (8/100, better than 69% of ceramic grades). Machine in the green/bisque state (drill, turn, mill dry with carbide) allowing ~10–14 % firing shrinkage; fired parts require diamond grinding, lapping or laser/ultrasonic drilling.
Can Steatite be welded?
Not weldable — join by glass frit, ceramic cement, active-metal or Mo-Mn metallizing plus brazing, or mechanical clamping with compliant gaskets.
What surface finishes work on Steatite?
Fired surface is naturally smooth and can be glazed for tracking resistance; ground/lapped for flatness, and Mo-Mn or thick-film Ag metallizing is used for solderable/brazable pads.
Can Steatite be formed, bent or molded?
Dry-pressed, isostatically pressed, extruded (tubes/rods) or injection/wet-pressed from talc–clay–flux batches, then fired at 1250–1350 °C; the vitrification window is narrow (~±20 °C), so temperature uniformity controls warpage and porosity.
What is the maximum service temperature of Steatite?
Steatite is rated for continuous use to about 1,000°C (1,832 °F). Strength falls off well before that limit — check the elevated-temperature data for load-bearing parts.
How much does Steatite cost?
Steatite is a high-cost ceramic ($$$$), pricier than about 98% of the materials FabDigit quotes. Part price depends far more on geometry, tolerance and quantity than on the raw stock — upload a CAD file for a live quote.
Sources
- ASTM D116 — Standard Test Methods for Vitrified Ceramic Materials for Electrical Applications (grades C-220, C-221) — ASTM International (2016)
- ASM Engineered Materials Handbook, Vol. 4: Ceramics and Glasses — ASM International (1991)
- Steatite technical ceramic property sheets — CoorsTek / CeramTec / Kyocera (2023)
- Technical ceramics property tables (steatite, magnesium silicate) — MatWeb (2024)
Property data is compiled from published supplier and standards handbooks and normalised for comparison; hardness values on non-Brinell scales are converted approximately for charting only. Manufacturability limits are FabDigit quote-engine defaults and may be relaxed by engineering review. Nothing on this page is a certification — request mill certs, CoC or material test reports with your order.