Gemstone Focus: Agate

Agate is very similar in its composition to Quartz (Silicon Dioxide), but can be identified from its distinctive curved banding which occurs in a variety of different ways. One of the most common and recognisable effects is the concentric banding, which is similar in appearance to the inside of a tree trunk when sliced through. Due to its porosity, Agate is often dyed to enhance this banding and popular colours include vivid blue, green and purple. This type of agate is most effective when sliced into larger pieces, which are often used simply for ornaments or book ends.


Moss Agate Cabochon

For the purposes of jewellery, it is the dendritic inclusions (moss or tree-like inclusions) which form the most interesting stones for setting. Moss Agate (above), as it is known, is usually transparent, grey or white in appearance, with the inclusions occurring in either dark green or black. They form the most fascinating organic network of strands which can either appear simply abstract or in some cases scenic, creating strange and haunting landscapes known as ‘Landscape Agate’. The joy of this type of inclusion is that you never know what you are going to find, with every stone being truly unique and interesting in its own way; it is nature at its beautiful best!

The other distinct way in which the banding can present itself in Agate is in the fortification formation. They appear as angularly arranged bands, and are thus named because of their resemblance to an aerial view of a fortress! The jagged white shapes that are present in this type of Agate are often quartz crystals, and like the dendritic inclusions, can form some spectacular scenic effects which make for some stunning stones. Again, this type of agate is often dyed to enhance the effect.


Fortification Agate (image source: Wikipedia)

Interestingly (if standard agate wasn’t diverse enough), there is also a type of fossilised wood called Agatized Wood, which is “fossilized wood that has had its organic matter replaced by agate” (Cally Hall (Gem Stones). Commonly called Petrified Wood, these fossils occur when trees become submerged in sediment which protects them from the decay caused by oxygen and various living organisms. Over time, ground water flows through the wood gradually dissolving the organic matter, and replacing it with mineral deposits which build up to form a solid mass. Often the outer appearance of the wood is retained, preserving details of the bark and wooden cellular structure which have effectively been turned to stone.

The most famous examples of Agatized Wood are to be found in the Petrified Forest in Arizona, USA. However, standard Agate is commonly found in locations across the world including China, India, Italy and Egypt along with its infamous home of Idar-Oberstein in Germany where it has been mined since the late 1400s. Despite its small size, Idar-Oberstein became famous for its rich sources of Agate, Quartz and Jasper which were mined and cut within the small town. As their own stocks diminished, the German lapidaries began to import rough stone from other countries to provide work for the townspeople, and to this day Idar-Oberstein is still renowned as one of the stone cutting Mecca’s of the world.

Agate is a relatively inexpensive stone with a great deal to offer so why not start searching for your own unique piece today? Explore the range of Agate Gemstones now available at Cooksongold here and add one to your next design.

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