Graulichite-(La), as yellow rhombohedral crystals with thin needles of agardite-(La). Field of view: 0.5 mm. Collection Georges Favreau, photo Pierre Clolus. The image is published in an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( https://creativecommons.org/licenses/by/4.0/ ). — Photo: Pierre Clolus · CC BY-SA 4.0
Agardite-(La)
Agardite is a mineral group consisting of agardite-(Y), agardite-(Ce), agardite-(Nd), and agardite-(La). They comprise a group of minerals that are hydrous hydrated arsenates of rare-earth elements (REE) and copper, with the general chemical formula (REE,Ca)Cu6(AsO4)3(OH)6·3H2O. Yttrium, cerium, neodymium, lanthanum, as well as trace to minor amounts of other REEs, are present in their structure. Agardite-(Y) is probably the most often found representative. They form needle-like yellow-green (variably hued) crystals in the hexagonal crystal system.
Intro adapted from Wikipedia (CC BY-SA).
Agardite-(La) is an IMA-recognized mineral species in the arsenate class, with the chemical formula LaCu²⁺₆(AsO₄)₃(OH)₆·3H₂O.
It crystallizes in the hexagonal crystal system (space group P6_3/m). It is a member of the Mixite structural group.
Key properties: specific gravity 3.65; optically uniaxial.
IMA symbol Agr-La, IMA status: approved, named in 1980.
Found in small amounts in the oxidized zone of hydrothermal mineralized breccia and polymetallic mineral deposits (Red Cloud mines, New Mexico, USA).
It is found associated with Fluorite, bastnaesite, barite, quartz (Red Cloud fluorite mine, New Mexico, USA); chrysocolla, malachite, azurite, mimetite, vanadinite, conichalcite.
By analogy to agardite-(Y), with its rare-earth content dominated by lanthanum.