Chemical composition -- A hydrated oxide of cesium, aluminum, beryllium, and boron.
Color -- Colorless to pale yellow or red.
Optics -- R.I 1.69.
Durability -- Hardness 8.5.
Crystal structure -- Isometric.
Specific Gravity -- 3.44.
Sources -- Madagascar is the primary source of this very rare material. Faceted gems are durable and attractive, but their rarity confines them to collections.