Luster is vitreous, resinous or adamantine. Specimens are translucent to opaque, but small crystals can be transparent. Crystals are rarely flattened or tabular. Twinning is common forming crosses and variously angled reentrant crystals. Typical habit is granular or massive with no distinct form.
Cleavage is perfect in one direction, poor in several other directions.
The result is often shards or acutely angled splinters. Fracture is uneven but gradationally converts to conchoidal with metamictation. Streak is white. A basal parting direction is sometimes noticeable. Crystal surfaces are often etched and pitted.