Apophyllite and Stilbite

Apophyllite

The crystals formed by apophyllite, which are very frequent, vary considerably in appearance. Indeed, flattened and thin, pseudocubic, bipyramidal, tubular or prismatic ones are found. The crystals can be colourless and transparent but also white and translucent or opaque, while the most sought-after ones show faint colourings of pink, blue, green or yellow. They have a lustre varying from vitreous to nacreous, melt at relatively low temperatures and are soluble in hydrochloric acid.

Apophyllite is of hydrothermal origin and fills the cavities of basaltic rocks, often in association with stilbite, scolecite, prehnite, calcite and analcime.

Its use is purely scientific and for collecting.

Stilbite

This mineral forms irregular, prismatic and often cruciform crystals. It sometimes also forms globular, radiating and sheaf-like aggregates. It can be colourless or whitish, but specimens with a yellowish or brownish colouring are also rarely found. Transparent to translucent, it has a vitreous and sometimes nacreous lustre. It melts in the blowpipe flame and is soluble in hydrochloric acid.

It generally forms in the cavities of volcanic rocks and is sometimes also present within metamorphic rocks and in Alpine-type hydrothermal veins.

Its use is purely scientific and for collecting.