Gadolinite
Gadolinite is a mineral that is reasonably rare is generally black and could be weakly radioactive if it contains Cerium (Ce), Lanthanum (La), Neodymium (Nd) and Yttrium (Y).
Gadolinite can be acquired from several localities worldwide: Ytterby, Sweden; ResarÄo Island and elsewhere in Norway; Val Bedretto, Ticino, Switzerland; Badgastein, Salzburg, Austria; Loughborough Township, Frontenac County, Ontario, Canada. In America, within the Clear Creek pegmatite, Llano County, Texas; near Hackberry, Mohave County, Arizona; near Lake George, Park County, Colorado
| Category: | Nesosilicate |
| Chemical Formula: | (Ce,La,Nd,Y)2FeBe2Si2O10 |
| Crystallography: | Monoclinic – Prismatic |
| Crystal Habit: | Crystals rough; typically prismatic, terminated, and many other forms, to 25 cm; commonly massive. |
| Twinning: | None |
| Cleavage: | None |
| Fracture: | Conchoidal or Splintery |
| Tenacity: | Brittle |
| Hardness (Mohs): | 6.5 – 7.0 |
| Density: | 4.36 – 4.77 (g/cm3) (when non-metamict) |
| Luminescence: | None |
| Radioactivity: | (Y): Not Radioactive
(Ce): Weak; GRapi = 44,145.76 (Gamma Ray American Petroleum Institute Units) |
| Color: | Black, greenish black, brown; grass-green to olive-green in thin fragments. |
| Transparency: | Transparent to Opaque |
| Luster: | Vitreous to Greasy |
| Refractive Index: | 1.770 – 1.820 Biaxial ( + ), Isotropic when metamict |
| Birefringence: | 0.0500 |
| Dispersion: | Strong; r < v |
| Pleochroism: | None |
