R´₄R´´₃Zr(SiO₃)₇, where R´ = K, Na, H, and R´´ = Ce(OH), Fe, Mn, Ca, and Zr(OCl) may replace SiO₂? A very complex mineral. ZrO₂ = 10·9-20; Cer = 0-5·2%.
Rhombohedral.
G = 3·0-3·1. H = 5-51⁄2. Red to brown; translucent. Double Refraction strong, -ve.
Various localities in Norway.
Eucrasite.
An altered [Thorite] (q.v.) containing E, Ca, Fe, Mn, Na, Ti, H₂O, etc. Cer = 14; Yttr = 5·9; ThO₂ = 36·0; ZrO₂ = 0·6%.
Rhombic (Paijkull). Amorphous, isotropic (Brögger).
G = 4·39. H = 41⁄2-5. Brownish black; opaque.
Near Brevig, Norway.