In hand sample, staurolite frequently occurs as twinned prismatic crystals known as “fairy stones” or “fairy crosses.” In thin section, it displays a poikiloblastic texture which people often liken to vomit spatter—gross, but effective.
Physical Properties |
|
| Chemical formula | Fe2Al9Si4O23(OH) |
| Class | Nesosilicate Isolated tetrahedra |
| Crystal system | Monoclinic |
| Habit | Prismatic |
| Color | Brown to black |
| Hardness | 7 to 7.5 |
| Specific gravity | 3.75 |
| Cleavage | Poor {010} |
| Fracture | Subconchoidal |
| Luster | Vitreous Resinous |
| Transparency | Translucent |
| Streak | White or gray |
Optical Properties |
|
| PPL | Poikiloblastic texture Clear to yellow or light brown |
| XPL | Max 1st order yellows Frequent quartz inclusions |
| δ | 0.013 |
| Twinning | Penetration Cruciform |
| after Perkins, 346 |
Staurolite in Hand Sample
Staurolite
Staurolite in muscovite staurolite schist
Staurolite in Thin Section
Thin Section GigaPans
Staurolite in plane polars
Staurolite in crossed polars
