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
Staurolite, Plane Polars
Staurolite displaying its characteristic yellow-brown pleochroism. Magnification: 40x To see this mineral in XPL, click here: https://youtu.be/O2gvC6wvqEg To…
Staurolite, Crossed Polars
Staurolite in crossed polars. Magnification: 40x To see this mineral in PPL, click here: https://youtu.be/ppJP74V6Z88 To explore this slide in PPL, click her…