The Mineral epistilbite

Epistilbite is a rare member of the zeolite group. It has a very similar chemical makeup to Stilbite, and can be difficult to distinguish from Stilbite. Epistilbite is named from the Greek Epi which means "similar" and Stilbite, due to the similarity of this mineral to Stilbite. Epistilbite is not dimorphous with Stilbite, despite its prefix Epi which often implies a dimorph. Interestingly, Epistilbite it dimorphous with a different zeolite, the rare Goosecreekite.

Chemical Formula

CaAl₂Si₆O₁₆ · 5(H₂O)

Composition

Hydrous calcium aluminum silicate

Color

Colorless, white, cream, tan, light yellow, light brown, gray. Rarely orange, orange-red, or pink.

Streak

Colorless

Hardness

Crystal System

Triclinic

3D Crystal Atlas
(Click for animated model)

Crystal Forms
and Aggregates

Crystals are often prismatic, with distinct chisel-topped terminations. Also globular and in hemispherical, ball-like formations. Other habits in include thin, tabular crystals and groups, columnar, in radiating clusters, and in jagged, haphazard crystals.

Transparency

Transparent to translucent

Specific Gravity

2.2 - 2.3

Luster

Vitreous, pearly

Cleavage

1,1

Fracture

Uneven

Tenacity

Brittle

In Group

Silicates; Tectosilicates; Zeolite Group

Striking Features

Crystal habits and association with other zeolites.

Environment

In air vesicles in volcanic basalt.

Rock Type

Igneous

Popularity (1-4)

Prevalence (1-3)

Demand (1-3)

Epistilbite AUCTIONS

POLYMORPHS

Goosecreekite

NOTEWORTHY LOCALITIES

Epistilbite is not a common member of the zeolite group, and good localities are few. Some of the largest crystals come from Berufjördur, Iceland, at Teigarhorn and Fossárfell. Sharp Epistilbite crystal group and aesthetic balls on matrix come from several localities in Maharashtra, India, most notably at Jalgaon, but also at Pune, Nasik, and Ahmadnagar. Small crystals with red inclusions come from Osilo, Sardinia, Italy. In the U.S., colorless micro crystals are found in the Puu o Ehu Quarry, Kailua, Oahu Island, Hawaii.

COMMON MINERAL ASSOCIATIONS

Quartz, Calcite, Heulandite, Mordenite, Stilbite, Apophyllite, Celadonite

DISTINGUISHING SIMILAR MINERALS

Stilbite - Different crystal formation.

epistilbite PHOTOS