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Learning Library

Geodes

A treasure chest full of mother natures finest creations.


A geode is a hollow rock, often constructed of limestone and some of the largest pieces ever discovered have been unearthed in Rio Grande do Sul. Inside these natural treasures often you will find Amethyst and Quartz.
Whilst Amethyst in the north of Brazil grows in large pegmatites, in the southern state of Rio Grande do Sul they always form inside geodes. Unlike many other gem-producing territories, Brazil is not on any fault line, therefore for thousands of years at a time there were no earthquakes, tectonic plate movements or massive changes within the Earth’s crust. This allowed the percolation of water and elements within the geode to grow crystals gently. This fairly tranquil environment allowed the Amethyst crystals to grow in an orderly formation, providing the gem with its well-known clarity.

With the insatiable growth in demand for geodes in China, Brazilian gem merchants are having to rebuild and remodel incomplete and broken geodes that in the past would have been broken up and sold to gem cutters for faceting into gemstones.

Whilst I was Brazil I visited Mauricio Lodi whose family business is one of the largest manufacturers of geodes. Sorry, did I say manufacturers? Well my terminology is quite apt: with demand out-stripping supply, his company has to almost construct geodes. Sure, each piece is extracted out of the ground as a genuine geode, but today they all go through a process of reconstruction.

After being sawn into two halves by a huge rotating diamond tipped saw, gem workers (I couldn’t find a better description) start to repair and repatch the geode. They glue in extra pieces of Amethyst in areas where the gem has not properly formed, they repair broken rims and re-fill the bore hole (the bore hole is drilled into the geode whilst in the host rock into which a probe is inserted to ascertain if it is worthy of extracting from the host rock). This reconstruction turns nice looking geodes into pieces of art.

I must admit before this visit, I had no idea about how much reworking went into geodes. Some pieces take three or four days to complete, but one of Mauricio’s managers told me that due to the huge increase in demand in Asia, the extra time spent on creating perfect pieces helped to push prices some five times higher than they were just a few years back.

On the outside of the geode they often add a layer of concrete to provide extra support and to help reshape the geode so that it can stand upright. Once dried the geode is painted a dark grey to make its appearance look as original as possible.
If the Amethyst does not have a pleasant hue, then the entire geode is put into a kiln and heat treated to turn the crystals into Citrine.

In the yard of the workshops, I came across an old gentleman who was gently hammering the outside of geodes as they were being unloaded from the back of a lorry delivering geodes fresh from the mine. As he tapped the gemstone he was listening to the echo. I was fascinated; I had never seen anyone listening to gemstones before! I asked Mauricio what he was doing; “He is listening to see if the geode has water inside, if it has we rename them “Water Agate” (the technical term is ‘enhydro Agate’). These completely sealed geodes have water trapped inside them that is hundreds of millions of years old. From what I understand, he sells these in the Chinese Market at a huge premium and the collectors keep them completely sealed, never to see the beauty hidden inside.  

Whilst we were talking about China I asked Mauricio how true it was that Chinese buyers were consuming most of the Brazilian geodes: he told me that three years ago he would always have hundreds of pieces in stock and yet today, his order book is always full three months in advance for deliveries to China. Although I was able to persuade him to part with a huge geode for my office, a wonderful piece weighing over half a tonne, virtually every other geode I saw in his warehouse was pre-sold to Chinese buyers.

Just before flying to Belo Horizonte, it’s the kind that every Tour Guide receives a back hander to stop the coach at, where the poor, unsuspecting tourist is subjected to a wide variety of locally produced goods, but all at highly inflated prices. Right there in the centre of the store was a geode very similar to the one I had just purchased. However the price was sixteen times more expensive than the piece I had just bought from Mauricio. Caveat emptor! (Buyer beware!) When you buy gemstones or jewellery anywhere around the world in a store where they sell local pieces, whether it be Larimar at an airport in the Caribbean, Ruby or Sapphire at Bangkok airport or geodes in Brazil, rather then getting the bargain you expect, the sellers prey on the consumers misinterpretation that they are going to receive a bargain because the gems are mined locally, when quite frankly they just rip you off!

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Steve at the church in Ametista do sul.