Habit: Yellowish or reddish brown to brown, pale yellow, pink or gray to nearly white. Crystals typically tabular or may be prismatic, equant or wedge-shaped; also granular or massive. Resinous to waxy luster, vitreous to adamantine, or can be dull to earthy; translucent to opaque. Grayish white.
Environment: An accessory mineral in granites, syenites and pegmatites and high-grade metamorphic rocks; also occurs in detrital river and beach sands. Associated with zircon, xenotime, titanite, thorite and columbite.
Etymology: From the Greek for "solitary," for its apparent rarity in its first known localities.