THE MINERAL EDENITE



Edenite is an uncommon amphibole mineral. It is related to the more well known amphibole, hornblende. Although hornblende is no longer an official mineral, it still serves as a general name for iron, magnesium, aluminum and calcium rich amphiboles of which edenite is one. Edenite had been referred to as "edenitic hornblende" before the name edenite was officially adopted as an official and distinct mineral.

Edenite is placed in the Tremolite Subgroup of the Amphibole Group. It is interesting to compare edenite to the more common tremolite; Ca2Mg5Si8O22(OH)2. A close look at the formulas of the two minerals shows that edenite contains both a sodium atom and an aluminum atom that is lacking in tremolite (as well as some iron). To compensate, tremolite has an extra silicon. This helps to illustrate edenite's environment of formation which tends to be sodium and aluminum rich granitic pegmatites and metamorphic skarns.

Edenite has a close cousin called ferro-edenite; NaCa2(Fe, Mg)5AlSi7O22(OH)2. The two minerals form a solid solution series in which the iron and magnesium substitute for each other. Ferro-edenite is the iron rich member hence the ferro designation, while edenite is the magnesium rich member. Edenite's formula is often written without the iron content implying a pure contentration of magnesium, but iron is almost always present in edenite.

Edenite was discovered in the 1830's while ferro-edenite was not discovered until the 1940's. Edenite was discovered in the rocks of the Franklin Marble, a formation that extends from the famous mines of Franklin, New Jersey into New York. Edenite gets its name from Edenville, New York, its type locality. Another similar mineral to edenite has been proposed called fluoro-edenite which is the same as edenite but fluorines would replace the hydroxides.

Edenite can form nice, well formed and sometimes complex monclinic crystals. Its translucent green specimens provide for the best examples of this species. Although not common, edenite is found around the world. It is unfortunately easily confused with other amphibole minerals such as tremolite, hornblende and fluorrichterite. Misidentification is a problem for this species as it has been identified from several localities only to have those specimens later attributed to other amphiboles, sometimes years later. Or possibly not recognized at first, only to be confirmed later if at all. Edenite is quite possibly more widespread than currently believed.

PHYSICAL CHARACTERISTICS:

 

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