Edenite is a double chain silicate mineral of the

amphibole Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

group with the general chemical composition NaCa₂Mg₅(Si₇Al)O₂₂(OH)₂. Edenite is named for the locality of Edenville,

Orange County, New York Orange County is a county located in the U.S. state of New York. As of the 2020 census, the population was 401,310. The county seat is Goshen. This county was first created in 1683 and reorganized with its present boundaries in 1798. Orange ...

, where it was first described.

Occurrence

Edenite has been found primarily in

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, cau ...

rocks, occurring in pods of other magnesium rich minerals within a

marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. Marble is typically not foliated (layered), although there are exceptions. In geology, the term ''marble'' refers to metamorpho ...

formation or with

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different ...

rich

lherzolite Lherzolite is a type of ultramafic igneous rock. It is a coarse-grained rock consisting of 40 to 90% olivine along with significant orthopyroxene and lesser amounts of calcic chromium-rich clinopyroxene. Minor minerals include chromium and alum ...

s from deep within the Earth's crust. Thus, finding edenite in the field can indicate high temperature regional metamorphism of the surrounding rocks.

Uses and importance

While edenite is not important for commercial or industrial applications, it is often studied because of its unique chemical substitution properties. Results from research performed on amphiboles have shown that edenite is particularly suited for fitting chloride anions into its chemical framework. This makes edenite a good candidate for use in chlorine isotope fractionation in amphibole-bearing rocks. Many synthetic variations of edenite are also used in geochemical research to produce a boron analogue of fluoroedenite.

Crystal habit

Edenite is a member of the

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic ...

crystal system In crystallography, a crystal system is a set of point groups (a group of geometric symmetries with at least one fixed point). A lattice system is a set of Bravais lattices. Space groups are classified into crystal systems according to their poi ...

and is in the crystal class 2/m (space group C2/m). This means crystalline edenite is symmetrical around a two-fold rotation axis that is then reflected across a mirror plane perpendicular to the long axis of the mineral.Klein, C., and Dutrow, B. (2007) The 23rd Edition of the Manual of Mineral Science, John Wiley and Sons, Inc. Hoboken, New Jersey, U.S..

Optical properties

Edenite is a biaxial positive mineral. When viewed in

thin section In optical mineralogy and petrography, a thin section (or petrographic thin section) is a thin slice of a rock or mineral sample, prepared in a laboratory, for use with a polarizing petrographic microscope, electron microscope and electron m ...

with a

petrographic microscope A petrographic microscope is a type of optical microscope used in petrology and optical mineralogy to identify rocks and minerals in thin sections. The microscope is used in optical mineralogy and petrography, a branch of petrology wh ...

, it is white-gray with pale green

pleochroism Pleochroism (from Greek πλέων, ''pléōn'', "more" and χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Backgrou ...

in plane-polarized light. Under crossed polars, its interference colors range from first order gray to first order blue.

References

{{Reflist Amphibole group Monoclinic minerals Minerals in space group 12