Goboboseb crystals showing crystal clear analcime – photos and specimens PdB
NaAlSi2O6-H2O, Hydrated Sodium Aluminium Silicate

The name of the mineral comes from the Greek word analkis that means weak.

Analcime is a zeolite and occurs frequently in basalts and other basic igneous rocks associated with other Zeolites.

Crystal system: triclinic (Pseudo-cubic)

The aluminosilicate framework of the crystal structure does not change in topology at all.  The reduction to various lower symmetries occurs because of slight changes in the ordering of Si and Al atoms and slight crumbling of the framework.  Macroscopically, the crystals always look pseudo-cubic, apart from the very slight non-zero birefringence and fine lamellar twinning visible in the polarising microscope, because the ordering and crumpling happens in different directions in different lamellae, and over the whole crystal it averages out.  Hence, the differences are far too slight to merit multiple species names, and analcime is a common example of a number of minerals which occur in multiple crystal system/space group varieties.  The crystal structure topology and maximum possible symmetry of the idealised structure are what really matters.  There is a slight analogy with hand specimen colour versus streak: a hand specimen can show a range of colours due to trace impurities, but these are diluted out in the small particles of the streak powder, so that only the true inherent colour of the material, much more constant, remains. (Andy Christy, 2010)

Some outstanding water-clear analcime crystals were found in the basalt of the Goboboseb area in Namibia near the Brandberg Mountain. Most of the crystals occur on the amethyst and smoky variety of quartz. Some of the quartz crystals are partly covered with analcime and some crystals have only a few scattered on.  Some analcime also occurs between epidote and prehnite and is found on top of the crystals as a secondary growth.

Analcime is not a rare mineral but is definitely rare from the Goboboseb area in Namibia and especially in crystals of this quality. It is hoped that this will not be the only occurrence, and that they will find more quality specimens.
Pieter de Bruyn, KM Minerals Kuruman. pieterd0@absamail.co.za