What is sillimanite schist?
sillimanite, also called Fibrolite, brown, pale green, or white glassy silicate mineral that often occurs in long, slender, needlelike crystals frequently found in fibrous aggregates. An aluminum silicate, Al2OSiO4, it occurs in high-temperature regionally metamorphosed clay-rich rocks (e.g., schists and gneisses).
What mineral is sillimanite?
Nesosilicate
| Sillimanite | |
|---|---|
| Category | Nesosilicate |
| Formula (repeating unit) | Al2SiO5 |
| Strunz classification | 9.AF.05 |
| Dana classification | 52.02.02a.01 |
Is sillimanite a gneiss?
Sillimanite is a rock forming mineral in a semi-pelitic gneiss where it forms fibers (sillimanite var. fibrolite) in amphibolite facies gneiss and small prismatic crystals in the granulite facies gneiss.
Is sillimanite high-grade?
Sillimanite from a variety of high-grade metamorphic rocks contains from 0-13 to 1-82 weight per cent Fe2O3 and less than 0-1 weight per cent TiO2. The iron is trivalent and substitutes for Al only.
What does sillimanite look like?
Colorless, white, yellow, brown, green, blue, gray. Comment: The pure material is nominally colorless, although it may appear pale brown in the fine-grained “fibrolite” variety.
What is sillimanite worth?
Sillimanite: average retail prices, Feb 2022
| Color Description, Occurrence | 1 ct. | 3 ct. |
|---|---|---|
| 062 – light yellowish Green; strong Alternative name, occurrence category: Common | $25.44/ct | $27.08/ct |
| 127 – very light very strongly greenish Blue Alternative name, occurrence category: Common | $33.11/ct | $35.25/ct |
How does sillimanite occur?
Disten or sillimanite, cordierite, and staurolite schists occur in conditions of high-degree metamorphism from pelite sediment, that is, shale, mudstone, and marl. These groups of schistose rocks are the product of high-degree regional metamorphism from organic matter-rich in clay sediments, or mudstone and shale.
How can you identify a sillimanite in a thin section?
- Relief: Moderate-High positive.
- Habit/Form: Sillimanite commonly occurs as slender prismatic crystals or as fine fibrous crystals called fibrolite.
- Color: Usually is colorless; sometimes may be pale brown, pale yellow, brown, green, dark brown, blue.
- Pleochroism: None; sometimes weak to moderate.
What is sillimanite refractories?
Sillimanite refractories are characterized of high refractoriness, very low coefficient of thermal expansion, high refractoriness under load (RUL) and mechanical strength with great resistance to thermal shock (spalling resistance), abrasion and slag corrosion.