Edenite (original) (raw)

Formula:

NaCa2Mg5(Si7Al)O22(OH)2

The minerals in the edenite group are defined with A(Na+K+2Ca)≥0.5 apfu and C(Al+Fe3++2Ti)≤0.5 apfu and with (OH), F or Cl in the W position.

Edenite is defined with
A position: Na dominant
C position: Mg dominant
W position: (OH) dominant

Colour:

White, grey, pale to dark green, also brown and pale pinkish-brown

Specific Gravity:

3.05 - 3.37

Crystal System:

Monoclinic

Name:

First mentioned in print in its mineralogical sense by Charles Upham Shepard in 1831, but he stated that the name was in common usage before 1831 and referred to the mineral's locality at Edenville, Orange Co., New York, USA. The first chemical analysis of edenite seems to be that published by Carl Rammelsberg in 1858.

NOTE: Endmember edenite is unstable, and near endmember compositions are not found in nature. Furthermore, all attempts to synthesize an endmember edenite have failed (Oberti et al., 2006). It has been found that Fe and F stabilize the edenite molecule and therefore edenite found in nature always contain significant amounts of Fe and/or F, although not always enough to qualify as ferro-edenite or fluoro-edenite.

The content of F is not always analyzed, and (OH) dominance is generally assumed when analyzing amphiboles. For the edenite root name group minerals, this assumption is probably incorrect in many cases. Therefore, it is probable that many of locality entries and photos of edenite in mindat are not correctly identified.

Chemically similar to pargasite (which has more Si and less Al).

RI values:

_n_α = 1.606 - 1.649 _n_β = 1.617 - 1.660 _n_γ = 1.631 - 1.672

2V:

Measured: 52° to 83°, Calculated: 84° to 90°

δ = 0.025

Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.

Dispersion:

weak to distinct

Comments:

in greens, blue-greens, and yellow-browns.

Crystal System:

Monoclinic

Class (H-M):

2/m - Prismatic

Cell Parameters:

a = 9.837 Å, b = 17.954 Å, c = 5.307 Å
β = 105.18°

Ratio:

a:b:c = 0.548 : 1 : 0.296

Unit Cell V:

904.58 ų (Calculated from Unit Cell)

Twinning:

Simple or multiple twinning parallel to {100}

- This locality has map coordinates listed. - This locality has estimated coordinates. ⓘ - Click for references and further information on this occurrence. ? - Indicates mineral may be doubtful at this locality. - Good crystals or important locality for species. - World class for species or very significant. (TL) - Type Locality for a valid mineral species. (FRL) - First Recorded Locality for everything else (eg varieties). Struck out - Mineral was erroneously reported from this locality. Faded * - Never found at this locality but inferred to have existed at some point in the past (e.g. from pseudomorphs).

All localities listed without proper references should be considered as questionable.