Alpha-Quartz vs Si (optical grade)
Glass · grade comparison
Alpha-Quartz and Si (optical grade) are both glass grades. Si (optical grade) is the stronger of the two: tensile strength 124 MPa (18 ksi) against 55 MPa (7.98 ksi) for Alpha-Quartz, about 125% more. Si (optical grade) is lighter (2.33 g/cm³ vs 2.65 g/cm³ for Alpha-Quartz) and Si (optical grade) is stiffer (130 GPa vs 87 GPa). On the shop floor, Si (optical grade) machines more easily (poor vs not recommended).
Alpha-QuartzChoose it when the part sees heat.
Si (optical grade)Choose it when strength drives the design, or when weight is the constraint.
Alpha-Quartz vs Si (optical grade): propertiesHow to read these bars
- One bar per material. A full bar is the highest value among all glass grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
How to read these bars
- One bar per material. A full bar is the highest value among all glass grades in the FabDigit library; each bar is drawn as a share of that.
- The better value (by the usual engineering direction) is in bold. Rows with no direction — density, thermal conductivity — have no bold.
- Values are typical room-temperature figures for the condition named on each card.
- Confirm against the certified mill or resin datasheet before design release.
Alpha-QuartzSi (optical grade)
Mechanical
Strength, stiffness, ductility and hardness at room temperature.
Elastic (Young's) Modulus
Shear Modulus
Bulk Modulus
Poisson's Ratio
Tensile Strength (Ultimate)
Compressive Strength
Flexural Strength
Shear Strength
Fracture Toughness (K_IC)
Hardness, Vickers
Hardness, Knoop
Same in both: Elongation at Break 0% · Hardness, Mohs 7
Physical
Density and transition temperatures.
Density
Melting Point (Solidus)
Refractive Index
Light Transmission
Same in both: Porosity 0%
Thermal
How each material carries heat and how hot it can run.
Thermal Conductivity
Specific Heat Capacity
Thermal Expansion (CTE, 20–100 °C)
Max Service Temperature (continuous)
Min Service Temperature
Electrical
Conductivity and insulation.
Electrical Resistivity
Dielectric Strength
Dielectric Constant (1 MHz)
Dissipation Factor (1 MHz)
Volume Resistivity
Chemical & Environmental
Corrosion and environmental resistance (0–100 scores).
Corrosion Resistance
Manufacturability
FabDigit workshop ratings (0–100 scores) — how each material behaves on the machine.
Machinability
Same in both: Polishability 95 / 100
Sustainability
Primary-production footprint per kilogram.
Embodied Energy (primary production)
Embodied Carbon (primary production)
Embodied Water
Typical Recycled Content
Common Calculations
Ratios derived from the values above.
Specific Strength (UTS / density)
Specific Stiffness (E / density)
Thermal Diffusivity
Thermal Shock Resistance Index
Strength versus weight
Yield strength against density for every glass grade in the FabDigit library; the compared grades are highlighted. Up and left is stronger for its weight.
Manufacturing and finishing
| Capability | Alpha-Quartz | Si (optical grade) |
|---|---|---|
| Default condition | — | — |
| Relative cost | $$$$ High | $$$$ High |
| Min. machined wall | — | — |
| Best machined surface | — | — |
Alpha-Quartz vs Si (optical grade) — frequently asked
Is Si (optical grade) stronger than Alpha-Quartz?
Yes. Si (optical grade) has a typical tensile strength of 124 MPa (18 ksi) against 55 MPa (7.98 ksi) for Alpha-Quartz — about 125% more.
Which is cheaper, Alpha-Quartz or Si (optical grade)?
Both sit in the same relative cost tier ($$$$, high); the part price will be decided by machining time, tolerance and quantity rather than by the material.
Which is easier to machine, Alpha-Quartz or Si (optical grade)?
Si (optical grade). Its machinability rates poor (20/100) against not recommended (6/100) for Alpha-Quartz.
Ready to make it?
Upload a CAD file and FabDigit prices the part in Alpha-Quartz and Si (optical grade) side by side — material, machining time, tolerance and finish in one quote. Certified material data ships with the order on request.
Typical handbook values for the conditions named above, normalised for comparison. Hardness on non-Brinell scales is converted approximately for charting only. Request certified data with your order for design-critical properties.