Heulandite

Heulandite is a type of zeolite mineral distinguished by its bright, glassy luster and elongated, well-defined crystal habit. It can be found in hydrothermal veins and cavities, typically in the form of white or clear aggregates that range from small blades to large crystals. 

Heulandite is one of the more common zeolite minerals. It has a very distinctive crystal form and has a noticeable pearly luster on cleavage surfaces. Since its original classification, Heulandite was always regarded as a single mineral species with a variable elemental makeup. In 1997, the Zeolite Subcommittee of the International Mineralogical Association divided this mineral into individual sub-species, thereby regarding Heulandite as a series of four members. The series is defined by the presence of several variable elements in the following order: calcium, sodium, potassium, strontium, and barium.

Color: White, colorless, beige, light yellow, brown, pink, and gray. Less commonly green, red, burgundy, orange, or black.

Hardness: 3.5-4 on Mohs scale.