Offretite, Limberg bei Sasbach, Kaiserstuhl, Baden (Germany) 
Offretite is a very common mineral at Limberg, mainly at Quarry I. This species was  for a long time only known from Mont Semiol, Loire,  France. The Limberg was one of the earliest other locations, described by Rinaldi et al. (1975).  Since then Offretite has been found on numerous  other locations worldwide.  Offretite crystals and aggregates are typical very small, only a few tenth´s of a millimeter and this may be the reason together with the difficulty to determine it, why its presence in many locations was not recognized  in the past. For many years also the Offretite from Limberg was considered as intergrowth with the very similar Erionite due to optical differences in the crystals, but recent investigations  by  WEISENBERGER & SPÜRGIN (2009) have shown that there is no substantial amount of  Erionite present.  Offretite, always very small forms different aggregates and habits which are shown below.
Limberg

Faujasite

Phillipsite

Chabazite

Offretite

Hyalite

Dolomite

Calcite

Aragonite

Montmorillonite

Paragenesis

Literature
Odffretite
Home Shaving brush like aggregates of  Offretite about 0,2 mm long from Quarry I.

Igel

pinsel
Offretite as radiating aggregates with some Hyalite. Field of view  about  1 mm. Aggregates of Offretite in Montmorillonite. Field of view about  1 mm.

barrel

auf Montmorillonit

Barrel-shaped Offretite. Field of view about 1 mm. Offretite-Aggregates on blue-black colored Montmorillonite.
 Field of view  about  1 mm mm

dippelendig

Klar

Reare shaving-brush like aggregate about 0.5 mm long. Clear hexagonal prisms of Offretite. Field of vie about 1 mm.

Igel

KANTEN

Coated aggregates of Offretite  Montmorillonite.
Field of view about 0.8 mm.
Offretite with Phillipsite -hemispheres. Field of view about 1.2 mm.
Druse
A vug in the Limburgite with small radiating aggregeates of Offretite. Field of view about 12 mm
The Limberg at Mindat.org The Limberg as a Geotope  with a map The Limberg for tourists

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© Volker Betz (2010). All rights reserved.