THE MINERAL EDINGTONITE

Chemistry: BaAl2Si3O10 - 4H2O, Hydrated Barium Aluminum Silicate.
Class: Silicates
Subclass: Tectosilicates
Group: Zeolites
Uses: As mineral specimens and chemical filters.
Specimens

Edingtonite is another example of the variety offered in the Zeolite Group of minerals. Like so many other zeolites, it is not a surprise to see that edingtonite is typically found in the cavities of volcanic rocks. Although not a colorful mineral, it does form some nice well-shaped crystals. It is an unusual mineral in that it has two polytypes or two phases that are not yet recognized as separate minerals. One type has a little more water content and a has an orthorhombic symmetry. The other type has a tetragonal symmetry. Both types have an overall tetragonal look to their crystals.

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

Edingtonite is one of only two zeolites to have barium in its chemistry. The other one is harmotome, with a formula of BaAl2Si6O16 - 6H2O. The heavy barium ion gives edingtonite the highest density of any zeolite. The larger amounts of water and the lower barium ion ratio lowers harmotome's density in relation to edingtonite.

PHYSICAL CHARACTERISTICS:

Color is colorless or white.
Luster is vitreous to dull.
Transparency: Crystals can be transparent but most commonly are just translucent.
Crystal System is tetragonal and orthorhombic.
Crystal Habits include blocky to prismatic or bladed crystals usually with a square cross-section, also massive.
Cleavage is perfect in one direction lengthwise.
Fracture is uneven.
Hardness is 4
Specific Gravity is approximately 2.8 (average, although heavy for a zeolite).
Streak is white.
Associated Minerals are manganite, heulandite, natrolite, stilbite and other zeolites.
Notable Occurrences include Ice River, Canada; Old Kilpatrick, Scotland and Bohlet, Sweden.
Best Field Indicators are crystal habit, density and associations.