Agate
Agate is the name for
some varieties of chalcedony, which is a form of micro-crystalline quartz, and
is a silicon dioxide. The names agate and chalcedony can be interchangeable,
although agate is usually the name for the banded varieties of chalcedony.
Agate is thought to
be named after the Silician River Achates, where some agates were found.
Agates can be transparent to opaque in a rainbow of colours, with concentric
layers of banding. Blue and green agates are the rarest.
Descriptive names such as moss agate, picture agate, crazy lace agate and blue lace agate are among
some of the varieties.
Each individual agate
forms by filling a cavity in its host rock, usually volcanic rock. It is
formed as a round nodule, sometimes with tiny crystals within the stone, called
drusy. Agate is a fairly hard stone, ranging from 6.5 – 7.0 on the Mohs'
scale.
Agate is found all
over the world including Africa, Egypt, Italy, Germany, Mexico, Brazil, India, Nepal and the USA. The
mining of agate in the Nahe river valley in Germany gave rise
to the world famous cutting centre of Idar-Oberstein.
Agate was discovered
by Stone Age man in France around 20,000-16,000BC and was used for
tools. From around 3000 BC Agate was used by the Egyptians for seals, ring
stones and a variety of different vessels. As a talisman or amulet in ancient
times, agate was highly valued. It was thought to protect the wearer from
thunderstorms, to quench thirst and gives powers of oratory.
Agate is an alternative birthstone for May and is also associated with the zodiac sign of
Gemini (May 21 – June 20).