Chemical composition -- A hydrated sodium aluminum phosphate.
Color -- Very light to medium tones of yellow or yellow-green.
Optics -- R.I 1.60-1.62.
Durability -- Hardness 5.5. Brittle. A little too fragile for most jewelry use.
Crystal structure -- Monoclinic.
Specific Gravity -- 2.98-3.0.
Sources --Brazil is the sole source of gem material. Although some large stones have been cut, most are under 5 carats.