both KFe3[(OH)3|SO4]2 to Alunite Super Group

 

Jarosite is linked to Alunite-Group. Also mixed crystal series with Alunite are possible but the light yellow color is more typical for Alunite - here on top of the surface of black Phlogopite, typicall for Laacher See area. 

Pure Natrojarosite is very rare.

The Jarosite will be find in oxidation zones where volcanic glass made a glazure in golden color on top of the crystals inside the xenoliths.  Together with Jarosite / Alunite the beautiful glass spots made nice effects at surface.