This is a thin section of radial growths of Baryte (or Heavy Spar).
This slide shows plumose (literally like feathers) interference structure.
In thin-section it is similar to other sulphates but can be distinguished by its straight extinction, moderately high relief, small 2V and paragenesis.
- Crystals are often intergrown, rosettes, as demonstrated in this TS.
- Four cleavage directions.
- Interference colors rangeup to first-order yellow.
- Sometimes pale colors-brown in PPL with weak pleochroism.
Collected from a mineral vein in the Hope Valley, near Castleton, Derbyshire.