Allanite, called “orthite” in Europe, is one of the most common rare earth minerals. Up to 20% of it's weight may be rare earth elements, making allanite a pote — Photo: Shannon Heinle · CC0
Allanite
Also known as: Orthite.
Allanite (also called orthite) is a sorosilicate group of minerals within the broader epidote group that contain a significant amount of rare-earth elements. The mineral occurs mainly in metamorphosed clay-rich sediments and felsic igneous rocks. It has the general formula A2M3Si3O12[OH], where the A sites can contain large cations such as Ca2+, Sr2+, and rare-earth elements, and the M sites admit Al3+, Fe3+, Mn3+, Fe2+, or Mg2+ among others. However, a large amount of additional elements, including Th, U, Be, Zr, P, Ba, Cr and others may be present in the mineral.
Intro adapted from Wikipedia (CC BY-SA).
Allanite is a mineral group, with the chemical formula (Ca,Ce)₂(Al,Fe)₃Si₃O₁₂(OH).
It crystallizes in the monoclinic crystal system.
Key properties: Mohs hardness 5.5–6; typically brown or black or green.
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