The Rare Earths: Their Occurrence, Chemistry, and Technology

by Stanley Isaac Levy

Rhombohedral.

G = 3·38. H = 4. Brown; faces dull.

Kangerdluarsuk, Greenland.

Strüverite.

FeO,(Nb,Ta)₂O₅,4TiO₂. TiO₂ = 69-71%.

Tetragonal; angles very close to those of rutile.

G = 5·0. H = 6-7. Black; opaque.

Craveggia, Piedmont, Italy; and in Madagascar.

Tachyaphaltite.

An altered zircon, containing H₂O. ZrO₂ = 40-50%.