Agardite

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Agardite
Agardite-(Ce)-174233.jpg
A rich example of Agardite-(Ce) in the form of pistachio-green acicular crystals on contrasting matrix
General
Category Arsenate minerals
Formula
(repeating unit)
(REE,Ca)Cu6(AsO4)3(OH)6·3H2O
Strunz classification 08.DL.15
Crystal symmetry Hexagonal – dipyramidal, H-M symbol (6/m), space group P63/m
Unit cell a = 13.59 Å, c = 5.89 Å, Z = 2
Identification
Color Yellow green
Crystal habit Acicular
Cleavage None
Fracture Conchoidal
Mohs scale hardness 3–4
Luster Vitreous
Streak Greenish white
Specific gravity 3.7 (measured), 3.775 (calculated)
Refractive index nω = 1.725, nε = 1.81
Birefringence 0.085
Pleochroism yellowish green
References [1][2]

Agardite is a mineral group consisting of agardite-(Ce), agardite-(Nd), agardite-(La), and agardite-(Y). They comprise a group of minerals that are hydrous hydrated arsenates of rare earth elements and copper, which contain variable amounts of calcium and sometimes lead. Yttrium, cerium, neodymium, lanthanum as well as trace to minor amounts of other rare earth elements are present in their structure. Agardite-(Y) is probably the most often found representative. The general formula for the group is (REE,Ca)Cu6(AsO4)3(OH)6·3H2O. They form needle-like yellow-green (variably hued) crystals in the hexagonal crystal system.

They were first described in 1970 in the Black Forest, Germany. They were named after Jules Agard, a French geologist.

References[edit]

  1. ^ Agardite. Mindat.org
  2. ^ Agardite. Webmineral