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Large Single Edenite Crystal

The edenite Mineral Group

Edenite is a member of the extended Hornblende group. There are several variations of Edenite with different elemental substitutions. Some of these are recognized as individual minerals, thereby making Edenite a mineral group, with Edenite the dominating member. Edenite is named after the hamlet of Edenville, New York, the type locality where this mineral was first described.
Chemical Formula NaCa2Mg5Si7O22(OH)2
Composition Basic sodium, calcium, and magnesium silicate
Variable Formula NaCa2(Mg,Fe2+)5Si7O22(OH,F)2
The above formula encompasses all the recognized member minerals of the extended Edenite group
Color Light green, dark green, greenish-gray, gray, black. Rarely white, tan, or yellow.
Streak White
Hardness 5 - 6
Crystal System Monoclinic
Crystal Forms
and Aggregates
Crystals are mostly tabular or in platy groups. Also in rounded individual crystals that are equant in size. Rarely fibrous or acicular.
Transparency Translucent to opaque
Specific Gravity 3.0 - 3.1
Luster Vitreous
Cleavage 1,2 - prismatic
Fracture Uneven
Tenacity Brittle
Other ID Marks Fluoro-edenite may be strongly fluorescent.
In Group Silicates; Inosilicates; Amphibole Group
Striking Features Cleavage angles and environment
Environment In metamorphosed marble.
Rock Type Metamorphic
Popularity (1-4) 3
Prevalence (1-3) 2
Demand (1-3) 2


Edenite is the name of an individual mineral, as well as group name for a few similar Edenite-related minerals with slight variations of elements in their chemical formula. Edenite is the magenesium and hydroxyl-rich form of this series, and the other forms the recognized by the IMA as individual minerals are listed below.
 -  Variety of Edenite where iron replaces the magnesium content. Ferro-edenite is recognized by the IMA as a distinct mineral species with the following chemical formula: NaCa2Fe2+5Si7O22(OH)2
 -  Variety of Edenite where fluorine replaces some the hydroxyl content. Fluoro-edenite is recognized by the IMA as a distinct mineral species with the following chemical formula: NaCa2Mg5Si7O22(F,OH)2

Edenite is probably more common than perceived, and can sometimes be perceived as Hornblende and not further identified. Dark crystal groups of Edenite were found in the Franklin marble at Amity and Edenville, Orange Co., New York, and across the border in Franklin and Ogdensburg, Sussex Co., New Jersey. In Canada, large crystals have come from several localities in Wilberforce, Monmouth Township, Haliburton Co., Ontario. Small crystals were also found in Mont Saint Hilaire, Quebec.

Calcite, Tremolite, Phlogopite, Biotite, Graphite, Scapolite

edenite PHOTOS
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