Agate
From The Gemology Project
Agate | |
---|---|
Chemical composition | Silicon dioxide SiO2 |
Crystal system | Trigonal |
Habit | Aggregate |
Fracture | Conchoidal |
Hardness | 6.5-7 |
Refractive index | 1.535 - 1.539 |
Specific gravity | 2.60 |
Lustre | Vitreous |
Agate is a variety of banded microcrystalline quartz, or chalcedony. There are countless varieties of agate usually named after their physical characteristics or location of origin. The layers of agate form as layers of chalcedony line a cavity (or vug) in a host rock. Since the twelfth century, agate has been attributed with the power of improving one's disposition as well as their eyesight. These beliefs still carry on today. One claim for agate was stated in The Book of Saxon Leechdoms written in 1864, where it was written that agate prevents harm from thunder, sorcery, demonic possession, poison and drunkenness!