Heulandite (calcium, sodium, potassium alumino-silicate with water) View 2 (back)

An attractive group of lustrous, orange, diamond-shaped crystals arranged in radiating sheaves. Heulandite is in the group of minerals called 'zeolites', from Greek words meaning 'boiling stone', they froth and bubble when losing water under strong heating. Zeolites have an unusual internal structure of parallel channels which makes them useful as molecular filters.

View of heulandite from behind