Chemical composition -- A silicate of potassium and calcium, also containing fluorine and water.
Color -- Mostly colorless or pale shades of yellow or green. Rarely dark green. Stones can be colorless in the extreme.
Optics -- R.I 1.53-1.54.
Durability -- Hardness 4.5-5. Brittle. Not very suitable for jewelry use.
Crystal structure -- Tetragonal.
Specific Gravity -- 2.3-2.5.
Sources -- Scattered locations, the most notable being near Bombay, India, where some dark green crystals are found. Apophyllite is seldom seen except in comprehensive collections.