Zeolite

This term covers a group of minerals that can grow in association with calcites and quartz - and with each other - often combined in a single specimen. This can make them hard to identify as individual minerals, although their colour, growth habit and structure (e.g. acicular or needle-like prismatic crystals, flattened platy, fanned or tabular crystals) can aid identification. The most commonly identified zeolites are:
HEULANDITE: Often ‘blocky’ diamond-shaped, trapezoidal or ‘coffin- shaped’ crystals, sometimes producing a crust of curved pearly faces – commonly coloured white, pink or peach.
NATROLITE: Often needle-like crystal, commonly clear or coloured white or pale peach. May also form square prisms.
STILBITE: Typically thin tabular crystals that grow in flattened elongated sheaths along an axis, often double ended like a bow-tie. Twinned, cruciform and penetration clusters are also common. Usually coloured pearly white, but also yellow, pink, peach or orange.

Zeolites may also be found in combination with other crystals, including:
APOPHYLLITE: Crystals are usually clear, white or pale green; and may be cubic or have pyramidal terminations.
SCOLECITE: Crystals are usually clear or white, long and delicately needle-like, often with a common core, so that the clusters can appear almost spherical.
CAVANSITE: Crystals are platy or needle-like, bright ‘neon’ blue and small, usually forming in tiny spiky spherical clusters. Like all such groupings the specimen concerned will combine the attributes of each of the individual minerals.