An accessory mineral in
granite, granite
pegmatites,
syenites; around
fumaroles; in
carbonatites and alkaline
intrusives. Economic deposits in low- to high-temperature hydrothermal veins and stratabound deposits; a cement in
sandstones (
Anthony et al., 2001—2005). There are faceted specimens over 3900 carats (
Arem, 1987: 99).
