• Chemistry: approximately (K2, Na2, Ca)MgAl8Si28O72 - 28H2O, Hydrated Potassium Sodium Calcium Magnesium Aluminum Silicate
  • Class: Silicates
  • Subclass: Tectosilicates
  • Group: Zeolites
  • Uses: Mineral specimen and chemical filter.
  • Specimens

Erionite is one of the rarer zeolites, a popular group of minerals to collect. Erionite has been challenged as a new mineral species. It was thought to be another rare zeolite named offretite. Offretite was named first and if erionite were proven in actuality to be offreite then offretite would have priority. First named gets priority in the mineral naming business. There is still some discussion on this matter in mineral parlance.

Erionite forms wool-like, fibrous masses in the hollows of rhyolitic tuffs and in basalts. The form is such that hardness measurements are impossible and basically irrelevant. The crystals not only look like wool they feel like wool as well. But they are brittle and stroking a specimen of erionite is a good way to ruin a specimen erionite, (see okenite). Erionite was first described by A.S. Eakle in 1898, as white woolly fibrous masses in cavities in rhyolite lava from near Durkee, Baker County, Oregon. 

Erionite'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 erionite can act as a chemical sieve, allowing some ions to pass through while blocking others.

Evidence suggests that erionite may be more toxic than serpentine asbestos. According to Dr. Bill Cordua, U. Wisconsin - River Falls:

This mineral is considered so hazardous that the EPA requires any one who intends to manufacture, import or process any article containing erionite to notify the E.P.A. 90 days in advance. ... It is not clear why erionite is so toxic. Other fibrous zeolites tested - mordenite and various synthetic zeolites - have so far not shown erionite's toxicity. Whether the cause is erionite's shape, some aspect of its surface reactivity, its resistant to dissolution in fluids in the lung, or some combination of these, is not known.
For more information, see "Deadly Erionite". Needless to say, we would recommend that any erionite specimens be secured in a sealed container, and exposure to erionite dust should be avoided.


  • Color is colorless or white.
  • Luster is vitreous.
  • Transparency: Crystals are transparent to translucent.
  • Crystal System is hexagonal.
  • Crystal Habits is limited to wool-like aggregates and crusts.
  • Hardness is unknown.
  • Specific Gravity is approximately 2.0 (very light)
  • Streak is white.
  • Associated Minerals are opal, calcite, heulandite, clinoptilolite, pyrite, thenardite, halite, celandonite, herschelite, phillipsite, chabazite, analcime and other zeolites.
  • Notable Occurrences include Durkee, Baker County, Oregon; Nevada, South Dakota and Arizona, USA and the Faroe Islands.
  • Best Field Indicators are crystal habit, low density, locality and associations.
ERIONITE specimens:
(hover for more info)
ERIONITE specimen eri-1
$ 25.00
Dims: 0.7 x 0.5 x 0.5" (1.7 x 1.3 x 1.2 cm)
Wt: 2 g
Rock Island Dam, Wenatchee, Washington, U.S.A.
A thin matte of pale-brown, almost wool-like Erionite lines some of the hollows inside the oolitic basalt or rhyolite tuff matrix of this small thumbnail piece. These "crystals" are so small as to be difficult to study even with a loupe- I cannot define much more than their color and their fine, needle-like habit. Its brown coloration is unusual, and is likely caused by iron staining. Other hollows contain crusts of darker offretite crystals that are very similar to Erionite in most aspects. The piece is protected inside a small plastic box.
no photo
eri-1 ($ 25.00)
Rock Island Dam, Wenatchee, Washington, U.S.A.


Copyright ©1995-2023 by Amethyst Galleries, Inc.