| Harlequin
precious opal with bright flashes of colour
Hematite
anhydrous iron oxide, red-brown to black
in colour
Hologram
three dimensional optical effect
Horsetails
type of grass (equisetalia) with high silica
content
Hyalite
colourless, glass-clear form of opal
Hydrophane
old term for a form of opal which becomes
translucent when immersed in water
Hydrothermal
deposits
deposits formed in the presence of water
at somewhat elevated temperatures |
