This page gives the full gilsonite specification — physical properties, chemical composition and elemental analysis — for raw, unrefined material as it comes from the mine. It also explains which property governs performance in each application, because the figure that decides a drilling fluid purchase is not the one that decides an ink or foundry purchase.
Read this first. The figures below describe gilsonite before processing. Every end use requires some degree of refining — sizing, sulfonation, or blending — and the finished specification changes accordingly. Always request the certificate of analysis for the specific grade you are buying rather than working from a generic table.
Physical Specification of Gilsonite
| Property | Value |
|---|---|
| Colour in mass | Black |
| Colour in streak or powder | Brown to dark brown |
| Moisture content | 0.5 – 1% |
| Specific gravity @ 77 °F | 1.04 – 1.06 |
| Hardness (Mohs scale) | 2 |
| Penetration | 0 |
| Acid value | 2.3 |
| Saponification value | 5.6 |
| Iodine number | 0 |
| Bulk density, lump | 40 lb/ft³ |
| Electrical resistivity | 4.0 × 1012 ohm-cm |
| Glass transition temperature (Tg) | 185 – 225 °F |
Why hardness 2 and penetration 0 matter together. Gilsonite is brittle, not plastic — it shatters rather than deforms at ambient temperature. Rolling the material between two drums gives the most consistent particle distribution for carbon production and for micronized grades. Crushers that work by impact tend to produce excessive fines.
Thermal and Viscosity Data
Volatility
| Condition | Weight Loss |
|---|---|
| 5 hours @ 325 °F | < 2% |
| 5 hours @ 400 °F | < 4% |
| 5 hours @ 500 °F | < 5% |
Brookfield viscosity
| Temperature | Viscosity |
|---|---|
| 375 °F | 55,000 cps |
| 400 °F | 22,800 cps |
| 425 °F | 6,600 cps |
| 450 °F | 2,800 cps |
Viscosity drops by a factor of roughly twenty across a 75 °F window. For blending operations this means mix temperature control matters more than mix time — a batch run 25 °F below target will behave very differently from one at specification.
Heat data
| Property | Value |
|---|---|
| Heat of combustion | 17,900 Btu/lb |
| Specific heat, solid phase | 0.52 Btu/lb/°F |
| Specific heat, liquid phase | 0.61 Btu/lb/°F |
Chemical Specification
| Property | Value | Method |
|---|---|---|
| Moisture | 0.5 – 1% | AGC method |
| Penetration (25 °C, 100 g, 5 s) | 0 | — |
| Colour in mass | Black | — |
| Sulfur | 3 – 3.3% | — |
| Specific gravity | 1.05 | — |
| Fixed carbon | 15% | — |
| Calorific value | 16,000 – 18,000 Btu/lb | — |
| Volatile combustible matter @ 1900 °F | 75 – 81% | ASTM D271 |
| Lustrous carbon content | 25 – 35% | — |
| Coking value | 20 – 25% | — |
For a deeper treatment of the molecular makeup behind these figures, see gilsonite chemical characterization and gilsonite molecular structure. Trace metal content is covered separately in gilsonite metal content.
Typical Elemental Analysis
| Element | Weight % |
|---|---|
| Carbon | 84.9% |
| Hydrogen | 10% |
| Oxygen | 1.4% |
| Nitrogen | 0.01% |
| Trace elements | 0.1% |
Which Property Matters for Which Application
A specification table on its own does not tell a buyer much. What matters is which single figure governs performance in the application at hand:
| Application | Controlling Property | Why |
|---|---|---|
| Drilling fluids | Softening point and particle size | The particle must soften at bottom-hole temperature to deform into microfractures and seal them |
| Oil well cementing | Specific gravity (1.04 – 1.06) | Low density allows slurry weight reduction without sacrificing compressive strength |
| Asphalt modification | Softening point and compatibility | Raises the binder’s high-temperature stiffness and resistance to rutting |
| Printing inks | Colour in mass, solubility | Deep black pigment body and clean dissolution in the vehicle |
| Foundry sand | Lustrous carbon (25 – 35%) | Lustrous carbon forms the reducing atmosphere that gives a clean casting surface |
| Paints and coatings | Volatility, colour | Low volatility keeps the film stable; the natural black avoids added pigment |
The most commonly misread figure. Buyers often compare suppliers on ash or sulfur alone. For drilling applications neither is decisive — softening point and particle size distribution govern whether the material seals a formation, and those are the figures worth specifying in a purchase order. See gilsonite in drilling fluids for the treating rates and grade selection that follow from this.
How the Specification Changes by Grade
The figures above describe raw material. Processing changes them:
| Grade | Particle Size | Specification Change |
|---|---|---|
| Lump | 2 – 50 mm | As-mined; bulk density approximately 40 lb/ft³ |
| Granulated | 0.5 – 5 mm | Higher bulk density, faster dissolution |
| Micronized | 45 – 150 µm | Greatly increased surface area; faster thermal response |
| Sulfonated | Powder | Water-dispersible; used in water-based muds |
Unprocessed gilsonite is hydrocarbon-soluble and disperses readily in oil-based muds. Water-based systems require the sulfonated or micronized treated grades.
Documentation Supplied
- Certificate of Analysis per shipment, covering the parameters above
- Safety data sheet (MSDS/SDS)
- HS code and customs documentation
- Third-party inspection (SGS or Intertek) on request
Frequently Asked Questions
Between 1.04 and 1.06 at 77 °F. This low density is the property that makes gilsonite useful in low-density cement slurries, where weight must be reduced without losing compressive strength.
Typically 3 to 3.3% in raw material. Sulfur content is naturally occurring and varies by deposit; a certificate of analysis for the specific shipment is the reliable figure.
Because it is brittle rather than plastic at ambient temperature. Unlike penetration-grade bitumen, gilsonite does not deform under a standard penetration needle — it shatters. This is also why it must be crushed rather than cut.
Yes. Every end use requires some refining — sizing, sulfonation or blending — and the finished specification differs from raw material. Particle size, bulk density and dispersion behaviour all change. Always work from the certificate of analysis for the grade being purchased.
Softening point and particle size distribution, not ash or sulfur. The particle must soften at bottom-hole temperature and bridge the pore throats or microfractures present in the formation. Those two figures should be stated in the purchase specification.
Twenty-five to thirty-five percent in raw gilsonite. In foundry sand systems, lustrous carbon forms the reducing atmosphere at the metal-mould interface that produces a clean casting surface. It is the controlling figure for foundry buyers.
Request a Certificate of Analysis
Specification sheets, samples and quotations for lump, granulated, micronized and sulfonated grades. Supplied from Dubai and Ankara offices.
Related pages: What is Gilsonite? · Gilsonite Properties · Gilsonite in Drilling Fluids · Technical Advantages · Gilsonite Price
