This is a condition found in radioactive minerals and results from the destructive effects of its own radiation on its crystal lattice. The effect can destroy a crystal lattice completely while leaving the outward appearance unchanged. Thorogummite is believed to be formed from thorite by hydration which is facilitated by metamictation. Specimens of thorite generally come from igneous pegmatites and volcanic extrusive rocks, hydrothermal veins and contact metamorphic rocks as well as small grains found in detrital sands. Crystals are rare, but when found can produce nicely shaped short prismatic crystals with pyramidal terminations.
Color is normally black, but also brownish black, orange, yellowish-orange and dark green.
Luster is resinous. Crystals are opaque. Crystal Habits include short prismatic crystals with a square cross-section and simple pyramidal terminations. Also massive, embedded irregular grains and reniform. Cleavage is poor, in two directions lengthwise, but is rarely seen.