• Chemistry: CaAl2Si6O16 - 5H2O, Hydrated Calcium Aluminum Silicate
  • Class: Silicates
  • Subclass: Tectosilicates
  • Group: Zeolites
  • Uses: Mineral specimen and chemical filter.
  • Specimens

Epistilbite is one of the rarer zeolites, a popular group of minerals to collect. Epistilbite commonly forms in the petrified bubbles (called vesicles) of volcanic rocks that have had a slight amount of exposure to metamorphism. It also forms in some pegmatites. Epistilbite's name means over stilbite perhaps in allusion to crystals of epistilbite that form over crystals of stilbite, a closely related zeolite. Epistilbite has similar crystal habits to stilbite although it rarely forms the large, impressive clusters that has made stilbite so famous.

Epistilbite's structure has a typical zeolite openness that allows large ions and molecules to reside and actually move around inside the overall framework. The structure actually contains open channels that allow water and large ions to travel into and out of the crystal structure. The size of these channels controls the size of the molecules or ions and therefore a zeolite like epistilbite can act as a chemical sieve, allowing some ions to pass through while blocking others.


  • Color is colorless, white, pink and reddish.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is monoclinic; 2/m
  • Crystal Habits include tabular to prismatic crystals, sometimes fibrous and radiating. Twinning is common with the interpenetration twin forming a cruciform (cross) shaped crystal.
  • Cleavage is perfect in one direction.
  • Fracture is uneven.
  • Hardness is 4.
  • Specific Gravity is approximately 2.2 - 2.3 (very light)
  • Streak is white.
  • Associated Minerals are quartz, beryl, calcite, yugawaralite, heulandite, stilbite and other zeolites.
  • Notable Occurrences include Poona, India; Berufjord, Iceland; Osilo, Sardinia, Italy; Isle of Skye, Scotland and in pegamtites at Bedford, New York and in the basalts of Hawaii, USA
  • Best Field Indicators are crystal habit, low density, locality and associations.
EPISTILBITE specimens:
(hover for more info)
EPISTILBITE specimen ept-1
$ 183.00
Dims:3.1x1.9x1.2" (7.9x4.8x3.0 cm)
Wt: 2.1oz. (60g)
Jalgaon, Maharashtra state, India
This specimen consists of a geode-like cavity in basalt matrix. Within the cavity are several radial sprays of epistilbite crystals. There is no noticable damage, and individual blades of the epistilbite show excellent monoclinic form. I found this to be a quite impressive and aesthetic specimen.
no photo
ept-1 ($183.00)
Jalgaon, Maharashtra state, India
EPISTILBITE specimen ept-2
$ 60.00
Dims:2.0x0.8x0.7" (5.1x2.0x1.8 cm)
Wt: 0.4oz. (12g)
Osilo, Sassari, Sardinia
The vuggy basalt matrix of this specimen serves as host for an excellent small prismatic crystal of epistilbite. The cavity is lined with white drusy quartz. The epistilbite, a reddish-brown color, contrasts nicely with the quartz. The crystal is small, measuring only 0.1" (0.3cm). A loupe yields a good view of this monoclinic mineral. There is no visible damage to this specimen.
no photo
ept-2 ($ 60.00)
Osilo, Sassari, Sardinia
EPISTILBITE specimen ept-3
$ 125.00
Dims: 2.74x2.34x1.76" (6.95x5.94x4.46cm)
Wt: 6.62oz (187.3g)
Jalgaon, Maharashtra, India
This is a beautiful specimen, displaying a large, round cluster of epistilbite in a cavity of the host rock. The individual crystals are colorless and transparent, and have a diamond-shaped cross section with roof terminations. They are neatly organized into a (partial) spherical cluster that appears white due to the interaction of the individual crystals. This cluster rests on a crust of a very dark greenish-black mineral, organized as tiny balls with a radial growth pattern. Under a loupe, it reminds me of some barite or selenite balls, or of hematite, but I do not believe it is any of these, given its origin. If you recognize it, please let me know! There are two other spots on the specimen with exposed epistilbite and this green-black mineral, but these areas are incomplete.
no photo
ept-3 ($125.00)
Jalgaon, Maharashtra, India


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