Opal (quartz)

Appearance:

Transparent/opaque; white, grey, blue, green, orange

Common variations...

White opal (milky opal), Black opal (dark grey, dark blue, dark green or black), Fire opal (orange), Common opal (opaque, mono-coloured), Hyalite (colourless, transparent opal), Wood opal (agatised wood), Honey opal (yellow), Prase opal (apple green, sometimes known as Chrysopal), Wax opal (yellow-brown), Hydrophane (transparent precious opal that has absorbed water)

Esoteric beliefs and associations...

Associated with the month of October, and with the God Cupid. White Opal encourages protection, purification and inner peace. Dark blue often attracts changes of circumstances and psychic ability. Green Opal has a weak (but observable) influence over matters of employment, money, growth and fertility. Orange colouration is often linked with energy, stimulation and stamina (both physical and spiritual), and the ability to cope in times of crisis.

Physical properties...

Chemistry	Hydrous silicon dioxide
System/Structure	Amorphous (kidney/grape shaped aggregate)
Refractive Index	1.440 - 1.469
Specific Gravity	1.98 - 2.20
Mohs' Hardness	5.5 - 6.5