Agardite

Agardite is a mineral group consisting of agardite-(Ce), agardite-(Nd), agardite-(La), and agardite-(Y). They comprise a group of hydrous calcium, copper arsenate minerals which contain variable amounts of the rare elements cerium, neodymium, lanthanum and yttrium as well as trace to minor amounts of other rare earth elements. The general formula is (Ce,La,Nd,Y,Ca)Cu₆(AsO₄)₃(OH)₆·3(H₂O). They form needle-like yellow green crystals in the hexagonal crystal system. The Mohs hardness is 3 to 4 and the specific gravity is 3.72.

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

References

• Mindat.org
• Webmineral data