Crystals are often modified by secondary faces with pairs of triangular faces very common. Prismatic and acicular forms are also known and are difficult to identify as heulandite. In aggregate specimens this face can be oriented upward producing a crust of curved pearly faces or it can be oriented to the side where the tops of the crystals jut out like the roof tops of a suburban community. Crystals can be simple or complexly modified by a variety of prism and pinacoid faces. Cleavage is perfect in one direction parellel to the prominent pinacoid face.
Fracture is uneven.
Hardness is 3.5 - 4, maybe softer on cleavage surfaces. Streak is white. Associated Minerals are extensive and include quartz , calcite , apophyllite , barite , pyrite , prehnite , pollucite , tourmaline , scolecite , analcime , chabazite , ferrierite , mordenite , laumontite , natrolite , stilbite and other zeolites . Best Field Indicators are crystal habit, density, cleavage, luster and associations. 1995,1996,1999 by Amethyst Galleries, Inc.