Allanite

Formula: (Ce,Ca,Y,La)₂(Al,Fe⁺³)₃(SiO₄)₃(OH)Mohs scale hardness: 5,5-6Specific gravity: 3,5-4,2 g/cm³Rare earth elements: Y, La, Ce^{Rare earth content, %: Ce}2^O3 ^{0–6; La}2^O3 ^0–7Y2^O3 ^0–8Other constituents, %: BeO 3.8; also ThO2Allanite (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. A large amount of additional elements, including Th, U, Zr, P, Ba, Cr and others may be present in the mineral. The International Mineralogical Association lists three minerals in the allanite group, each recognized as a unique mineral: allanite-(Ce), allanite-(La) and allanite-(Y), depending on the dominant rare earth present, cerium, lanthanum or yttrium.Allanite contains up to 20% rare earth elements and is a valuable source of them. The inclusion of thorium and other radioactive elements in allanite results in some interesting phenomena. Allanite often has a pleochroic halo of radiation damage in the minerals immediately adjacent. Also highly radioactive grains of allanite often have their structure disrupted or are metamict. Allanite is usually black in color, but can be brown, brown-violet. It is often coated with a yellow-brown alteration product, likely limonite.

References

1. https://en.wikipedia.org/wiki/Allanite

2. https://books.google.cl/books?id=jPskAQAAIAAJ&pg=RA4-PA13&lpg=RA4-PA13&dq=Green+Cove+Springs+Mine+monazite&source=bl&ots=8xH_PV9MoG&sig=MkXPfqzQ6OM4zmU2OWc-eHL2-GQ&hl=ru&sa=X&ved=0ahUKEwj6-bG1mfbMAhUDE5AKHYGfCWsQ6AEIKDAD#v=onepage&q&f=false