Amethyst Geodes – An Introduction
With its vibrant purple hues, lustrous crystal forms, relative abundance and modest cost, Amethyst is undoubtedly one of the world’s most popular captivating semi-precious gemstones. The word “Amethyst” stems back from the ancient Greek word “Amethystos” which translates to sustaining a sound, sober mindset.
Perhaps the most impressive of all the Amethyst varieties is the Amethyst geode. These hollow gem-filled bubbles, have adorned collections the world over for hundreds of years. Varying in size from a few centimeters to several meters in diameter, they represent the absolute pinnacle of Mother Nature’s creation.
Geology & History of Mining Amethyst Geodes
Since its discovery in the early 19th century, Brazil has long since been the global leader in the production of Amethyst. Although there are numerous mining regions across Brazil, our focus is on Rio Grande Do Sul, which to this day, remains the world’s premier supplier of Amethyst geodes.
Rio Grande Do Sul is situated in the southernmost state of Brazil; bordering on Uruguay and Argentina. Approximately 130 million years ago, the region experienced substantial volcanic activity. Thick, viscous flows of lava flooded the region in successive layers which hardened into dense, fine-grained basalt over a millennia. Within these solidifying lava flows, large gas pockets became entombed within the basalt. Over time, hydrothermal fluids enriched in all the elements required for amethyst production permeated into these cavities. Slowly but surely, these fluids began to cool, and crystalise out the gorgeous amethyst lined geodes we admire today.
Rio Grande Do Sul’s rich mining history dates back to the 1820’s when immigrants from the Hunsruk region near Idar-Oberstein — what is now referred to as Western Germany. When Amethyst was first discovered, it was these immigrants who recognized the potential economic wealth of the region and commenced mining and shipping Amethyst back to Idar-Oberstein in the form of gem and specimen rough. Much of the mining was initially carried out by pick and shovel artisanal practices. This was incredibly hard work by any measure, however justified with the current economic value of Amethyst at the time. Prior to this discovery, Amethyst was comparatively scarce, with only a few economic deposits known to exist which primarily resided in Russia.
It is the descendants of those early pioneers that still reside in Rio Grande Do Sul today. Generations of expertise in mining methods have perfected the mining process of these enormous, yet inherently fragile natural entities.
Amethyst Geodes – How They Are Mined
Current mining practices now incorporate an amalgamation artisanal mining methods and more modern techniques by the use of large machinery and explosives. Mining will commence either as an open pit or underground operation with the removal of waste rock, which is essentially the solidified basalt with no discernible Amethyst.
Only the most experienced of miners will know when they are nearing closer to an Amethyst geode, with subtle colour changes to the exhumed rock and associated mineralogy. Once a geode is located, the mining process slows down to a snail-pace. Because these fragile geodes are encased in solid rock, painstaking care must be taken to carefully chisel away the encasing rock until the surface of the amethyst geode is exposed. This process can take days to weeks, depending on the size of the geode. At this point, a very small hole is drilled within the geode and small telescopic camera is inserted. With this relatively modern method, the miner can ascertain the grade of the geode, which is primarily governed by the saturation of colour and crystal size. The geode is then chiseled away from the remaining encased rock and carted back to the surface where the geode will undergo cutting and preparation for sale.
Amethyst Geodes – How Are They Prepared for Display
The geodes are then slowly cut in half with the use of a large diamond blade. This is a slow process, where the diamond blades slowly grinds through the geode; a process that can take several hours in itself. It is only then that the geode is separated into two halves and sees the light of day for the first time in millions of years!
Both halves are then polished to remove any cut marks. The outside of the geode is then coated with a thin bonded layer of mortar to fill in any unwanted fissures or cracks which helps stabilize the geode. For exceptionally large geodes, rebar is used before the mortar process to ensure that the geode has enough structural integrity to stand up on its own weight.
After this process, the stabilized surface is then painted to colour match how the geode would have looked in its natural state, which is a dark green colour attributed to the iron rich mineral Celadonite.
The geode is now ready for its journey. From the pride and joy of a private collection to a spectacular display within a museum of natural history, the Amethyst geode will always hold a special place in our hearts that will transcend scientific and cultural lore.