GMT   
Search:
Home > Information > Gemstone Index > Chalcedony > Agate, Jasper & Mookaite

Chalcedony (see also Onyx, Sardonyx and Quartz)

Chalcedony is cryptocrystalline quartz, formed at low temperatures in volcanic cavities, the crystals are so tiny that en mass they appear more like porcelain.

Chalcedony is a form of chert and was known and used by prehistoric man, for weaponry, tools and decoration.

Agate and Jasper

Fortification agate resembles the the ariel view of an ancient hill fort.

Agate and jasper come in a whole colour range, which explains the popularity of this stone. Due to the close similarities of agate and jasper, the name is sometimes interchangeable.

Agate is mainly found in basalt geodes of rock, distinctive bands are formed when basalt lava solidifies quickly trapping bubbles within the stone, as the lava cools silicate minerals escape into these bubbles and form a gel, (a little like opal); as the iron and maganesium compounds from the surrounding rock are absorbed into the gel-like bubbles they form iron/magnesium hydroxide which hardens and forms the signatory bands of agate.

Fancy Jasper aka
Indian Agate.
Jasper, an opaque stone, lacks the bands of agate, it is found in both volcanic and sedimentary rocks and the colours come from a range of mineral impurities.

Sometimes jasper can replace the organic matter - as in 'petrified wood'.


|Structure: Triclinic|Composition: Sodium calcium aluminosilicate|Moh's Hardness: 7|

Mookaite

A comparatively recent 'discovery' from Australia.

This stone appears to have the same characteristics as the crypto-crystalline chalcedony, a personal favourite in a range of "hot" colours, brick red, lilac, mustard, coffee and cream.