General Information:
Chemical Formula:
Na2Mn8[Si11AlO29](OH)7·11(H2O)
Composition:
(Molecular Weight = 1,602.61 gm)
Sodium 2.87 % Na
Manganese 27.42 % Mn
Aluminum 1.68 % Al
Silicon 19.28 % Si
Hydrogen 1.82 % H
Oxygen 46.92 % O
Empirical Formula:
Na2Mn2+8Si11AlO29OH7·11(H2O)
Environment:
Miarolitic cavites in nepheline syenite. Probably isostructural with ganophyllite.
IMA Status:
Approved IMA 1982
Locality:
Big Rock Quarry, Little Rock, Pulaski County, Arkansas, USA.
Name Origin:
Named for R. A. Eggleton, Australian National University.
Physical Properties:
Cleavage:
[001] Perfect
Color:
golden brown.
Density:
2.76
Habits:
Radial - Crystals radiate from a center without producing stellar forms (e.g. stibnite), Acicular - Occurs as needle-like crystals., Prismatic - Crystals Shaped like Slender Prisms (e .g. tourmaline).
Hardness:
3-4 - Calcite-Fluorite
Luster:
Vitreous (Glassy)
Streak:
light brown
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