Scolecite is a hydrous calcium aluminum silicate. Scolecite is a member of the zeolite group. Scolecite forms a series with Natrolite and Mesolite. Scolecite is the calcium rich end member of the series. Scolecite and Natrolite can be very difficult to tell apart and may even exist together in a single crystal. This is an interesting specimen growing out of an almost transparent Calcite.