Heulandite

Heulandite ((Ca,Na)(Al2,Si7,O18) x 6H2O) can be white, greyish, colourless, greenish or red in colour. Lustre is vitreous, and pearly on the cleavage. Streak is colourless and hardness is 3 1/2 to 4. Cleavage is perfect in one direction. Heulandite usually occurs as coffin-shaped tabular crystals or can be radiating aggregates, foliated, globular or granular. In this sample, crystals are predominantly tabular to short prismatic and occur as densely intergrown, subhedral to euhedral aggregates. Individual crystals locally exhibit the characteristic flattened, approximately rhombic to “coffin-shaped” morphology associated with heulandite. Crystal surfaces exhibit vitreous to pearly lustre, with the aggregate displaying minor variation in crystal size and orientation. Pale peach colouration is locally concentrated within portions of the crystalline coating.