This entry was posted on Wednesday, November 5th, 2008 at 5:57 pm and is filed under Fountain information. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
Amethyst
The name amethyst comes from the Greek word “α-μεθηστos” which means not drunk. Roman emperors had used goblets made form amethyst geodes in the belief that the crystals would counteract any poisons and will keep them from getting drunk. The ancient Romans thought amethyst crystals to be different from quartz crystals. They thought quartz was water that had been frozen so hard and long that it would never melt away.
Amethyst is a variety of quartz and has basically the same chemical composition, atomic structure and physical properties of quartz, its chemical formula is silicon dioxide SiO2, with a hardness 7–lower in impure varieties on the Mohs scale, with a specific gravity of 2.65 g/cc, and a crystal habit 6-sided prism ending in 6-sided pyramid (typical). Books on geology and mineralogy usually lists it under quartz. The crystal system rhombohedral class 32, and the fracture is conchoidal. The bible mentions amethyst as one of the twelve stones in the breastplate of the High Priest and thus represented one of the 12 tribes of Israel of the middle East.
When the variety of quartz called amethyst is being formed, the water supplying the nutrients for the growing crystal carry some dissolved iron in its ferric (Fe+3) state. This is incorporated into the structure of the growing crystal. When the ferric iron is incorporated into the structure of the quartz crystal it forms color centers. Natural ionizing radiation in the ground then strips another electron from the ferric iron atom, this activates the color center which gives the amethyst its deep rich color.
That means that the color center absorbs all the colors except those in the purple/violet region which are transmitted and reflected to our eyes. Refractive index nω = 1.543–1.553 nε = 1.552–1.554, diaphaneity is transparent to translucent, the luster vitreous to glossy, and Birefringence +0.009 (B-G interval). The intensity and color of the amethyst depends on how much iron is in the quartz crystal, and where it is located in the atomic structure of the quartz, and the possible presence of aluminum which may impart a slightly smoky color to the amethyst. The melting point is 1650±75 °C, and the solubility H2O insoluble.
Where are Amethyst Geodes found?
Amethyst Geodes and crystals are found in over a thousand regions in the world that have produced amethyst crystals of one kind or another. Thunder Bay in Ontario Canada is well known for the modest examples of small drusy amethyst crystals found in that region. In South Carolina near the town of Due West where some awesome examples of amethyst have been found. Mexico is also well known to collectors for the areas by the town of Veracruz, and Guerrero that produce beautiful prismatic amethyst crystals. Most states and provinces in North America have several areas are known to produce amethyst crystals and geodes. The same can be said about all the other countries around the world, and I could fill up pages describing the kinds of amethyst that they have found in the past.
Only a few regions that are rich enough to be mined for amethyst geodes, and crystals on a regular basis. Most of these regions are mined almost exclusively just for the gems, and well crystalized specimens are rarely preserved even if they are found. Only a handful of regions are mined for awesome examples, and the miners keep a sharp eye out for any material which can be cut into these precious gems. Only a few amethyst geodes, and crystal examples with substantial amount of high grade gem material ever ends up on display, most will likely be hammered down into gem rough and cut into anonymous faceted stones for jewerly.
Where are most of the world’s Amethyst geodes produced?
The most productive regions in the world for amethyst examples, and agate nodules is in Rio Grande do Sul, the southern most state of Brazil. One could argue that this region has produced about 10 times more amethyst than any other amethyst region and perhaps as much as all other amethyst regions in the world combined togather. Many places in Rio Grande do Sul produce amethyst and agates, but today the big producer is the region around the small town of Amethista do Sul, near the larger town of Irai. This region is near the Argentine border and about 250 miles North-North West of Porto Alegre, which is the capital and largest city in Rio Grande do Sul.
This region has produced most of the amethyst geodes and agate during the last part of the 19th century and during the 20th century. The total production of the area can be measured by the kilotons. Gemologist’s place the current production of amethyst examples at 2 to 3 thousand tons per year. Originally the farmers of the region had found the amethyst and agate loose in the top soil of their fields, and on the hillsides. As time went on the richer areas of alluvial material were mined for agate and amethyst geodes. When the easily worked area began to run out, the miners began to work the host rock and produce material from open cut mines by drilling, and blasting the basalt. Today, most of the mining takes place in underground mines.
The geology of the region is mostly consists of sheet basalts thst are weathered into a rolling countryside with occasional rivers and streams. Today its a rich green farming area with corn and black beans fields. Sheet basalts are rock formations that form when cracks in the earths crust open and molten rock pours out over the earth’s surface like a big thick blanket. Each flow can be a few feet thick to over a hundred feet thick, and can cover over many thousands of square miles. Some of these flows occur over and over, building up over time to depths of many thousands of feet deep.
Basalt is an igneous rock, and those found in Southern Brazil are black to gray in color when broken or chipped. Some molten basalts are rich in gases and when they cooled they harden into rock. The gas bubbles are trapped inside the rock like air bubbles. In Rio Grande do Sul the size of the bubbles vesicles range from microscopic size to several feet in diameter less than 10 feet, and as much as fifteen to twenty feet high. These vessicles tend to be typically rounded, and taller than they are broad, flat on the bottom, and tapering to a narrower rounded top, very much in shape like the cone shape. Sometimes these cones become distorted along one or more axes or run together and sometimes vesicles with two or more cones togather have been found. The largest amethyst geode in the world was found in December 2006 in the Galerias Santiños Mine in Uruguay. It is named the “Empress of Uruguay” it’s weight is 2.7 tons, it Stands at 10′ 7″ tall, and the quality of amethyst is AA !
How are the Amethyst Geodes formed?
Basalts are porous, and over time, water laden with dissolved silica and other minerals migrate through the basalt formations, fill the vesicles and slowly form minerals of various kinds on the rock walls of these ancient gas bubbles. In the basalts of Rio Grande do Sul, the mineral that most commonly lines the walls of these vesicles is the variety of quartz called agate and then quartz crystals grow on the agate. These quartz crystals are irradiated with natural radiation in the ground which turns them into amethyst. When the vesicles become mineralized they are called amygdaloids. Some amygdaloids become filled entirely with minerals, typically the variety of quartz silica called agate.
Over millions of years the rocks containing these amygdaloids can weather away, and the if the minerals filling the amygdaloids are more resistant to weathering than the rock, these amygdaloids are left in the soil and on the surface of the ground, and they are called nodules. If the material in the amygdaloid was agate they are called agate nodules, however if the agate fills only part of the amygdaloid with its center still empty or hollow it is called an agate geode. Geodes are commonly more or less round and when you break them open they are hollow in the middle, and frequently lined with crystal formations, commonly know as quartz crystals. If the quartz is of the amethyst variety they are called amethyst geodes. In Rio Grande do Sul state, the miners remove the rock from around the amethyst geodes, by drilling and blasting the rock away as efficiently as possible today.
How do they locate Amethyst crystals?
Near the small town of Amethista do Sul, one particular basalt flow under the town has been found to be very rich with amethyst geodes, basalts flow is about 10 feet thick, and is just one of many layers sandwiched between others and is not much different in color or texture from them except that it has a lot more amethyst filed amygdaloids than the others. Like all of its cousins, this basalt flow is relatively flat laying, so once it is located the miners can easily track its properties on the hillsides or in the valleys walls. It also means that when the miners drive the tunnels into the basalt searching for the amethyst geodes, they can drive the tunnels level into the formations.
The tunnels are driven in to the basalt parallel to each other, and some tunnels have been driven about 800 feet into the basalt. Only naturally ventilation removes the fumes from blasting and the exhaust from the little diesel powered dump trucks needed to remove the waste rock form the mine tunnels. Ventilation is helped by the large number of little cross cuts or shafts that interconnect the tunnels. In rich areas, all the rock is removed except for the pillars or columns left in place help to keep the mines from caving in. Going underground in the mines is like being in a very large room with low ceilings and arched pillars.
Miners that are using rock drills powered by compressed air to drill holes into the basalt then blast it free using homemade blasting powder. More often when the miners are drilling, the drill will push in forward into the rock indicating the drill has gone threw a wall of an amygdaloid and into an empty space in the center of the amethyst geode. The drill steel rod with its carbide tip is backed out from the hole and a light is inserted to see the empty space. The miners light sometimes consists of a flashlight bulb soldered to wires that are connected to a truck battery. They use this light to try and get a good idea of the shape and quality of the amethyst geode that was found. Knowing how big and the shape of the geode will make removal of the geode easier.
If it contains only white quartz or very pale amethyst the decision may be to ignore it and just keep drilling and blasting instead of trying to carefully remove it in one piece from the basalt. The removal of amethyst geodes from the basalt may involve a little more careful drilling and blasting, this involves a lot of hand work for the miners. Pneumatic rock chippers or rock hammers are used to break away the surrounding basalt until the geode is freed up. The miners sometimes break the geode during this process. All geodes have natural cracks which are maybe worse during removal from the basalt. Each geode will have a drill hole in each one which is the testimony to its method of its discovery.
When the geodes are first removed from the basalt they look like olive green coneheads raging in its size from a few inches to 10 feet high. They are green in color, because of a thin green layer about 1- 2 mm, thick of a mineral called celadonite, which is one member of the mica group of minerals. This mineral is very soft and flaky and makes it easyer to break the basalt away from the outer walls of the geodes. Amethyst geodes are removed in a similar manner in northern Uruguay and they don’t have this coating of celadonite on their walls witch makes removing them in one piece from the basalt much more difficult. Even before the geodes are completely removed from the basalt, some miners use different kinds of super glues to help stabilize the geodes better. After the geodes are removed from the mine, more super glue may be used to help it survivel of the cutting, polishing and transportation.
The mines are where most of the geodes are sold in large lots, or batchs to some of the larger companies dealing in amethyst geodes. Most of these large companies are located in the city of Soledade, a few hours to the south of Rio Grande do Sul state. The geodes are usually transported in open trucks full with wood chips from the local saw mills. These wood chips make very good packing material which is used over again when the geodes are shipped out of Brazil to traditional markets of the USA, Europe and more recently Hong Kong, Taiwan as well as other places on the Pacific reagion.
The preparation process for Amethyst Geodes.
Most of the amethyst geodes are cut and polished, or prepared for sales to customers. Most of the geodes are put in diamond saws and cut in half lengthwise to produce two matching amethyst cathedrals halfs. Others, especially those with very thick walls are cut, or sliced perpendicularly into amethyst rings. The diamond saws vary in sizes, the largest of saws is huge that can use a blade about 10 feet in diameter. The cut surfaces are then sanded down, polished and sorted into various US$ per Kg categories.The large geodes are sanded by hand held sanding and polishing machines that look like auto body grinders “D.A. grinders” used for cars.
The prices increase with the intensity of the amethyst color, and the smaller sized geodes are more in demand than larger ones are. Small geodes about 12″ to 18″ range also cost more, with all other considerations equal. Geodes with good bilateral symmetry cost more and those with very thick walls, sell for less per Kg. Amethyst geodes that have very thick walls can weigh three times what another would geodes of the same size but with a thin walls. some geodes may have beautiful agate under their amethyst crystals. Others may have striking inclusions of golden cacoxenite needles in the amethyst or beautiful crystals of calcite or transparent gypsum crystals growing on the amethyst crystals. These factors will increase the value of the amethyst geodes.
Most people seek in Amethyst Geodes is to:
A, Have darker colored, brilliantly shiny amethyst crystals.
B, Have thinner walls, so they wont weigh much for less cost.
C, Have the amethyst crystals in good sizes and be well formed.
D, Have good symmetry of equil balance or regular form.
E, Be not be very large, because large ones weigh more and cost more.
F, To be free of cracks, and drill holes or other defects.
The reality of sales tackticks or tricks.
Less than one geode per thousand are free of any defects. You must assume that all geodes have been repaired or reinforced in some manor. The large companies that sell the amethyst geodes have developed methods of fixing defects on geodes to make them more salable. They fix up the drill hole by laying the amethyst geode in a big plastic bag thats filled with tiny tumbled stones, with the drill hole faceing down. They then fill the drilled holes with small crushed quartz fragments to the bottom level base of the amethyst crystals. They then take loose amethyst crystals that match the size and color of the ones in the geode and seat them in the crushed quartz and arrange them till they have get a good solid feel.
Then finally, they pour the epoxy resin over the loose amethyst crystals and saturate the crushed quartz in the hole, and let it set to lock the pieces in place. The cracks are reinforced with super glue that can easily be spotted from the outside of the geode, by the glue turning the olive green celadonite to an almost black in color.
Now the suppliers have taken to painting the outside of the amethyst geodes with a thin green plaster, covering up all drilled, filled holes and all the reinforced cracks, and defects on the walls. At a first glance this treatment looks like natural olive green celadonite coating. If you look very carefully polished front of a geode you may be able to see some of the obvious cracks in the amethyst geode. Cracks occur naturally in almost every amethyst geode found and may or may not correspond to any crack in the geode that has been reinforced with super glue. It is vary difficult to spot the glue repair inside an amethyst geode.
Another tricks used in selling amethyst geodes is to not show them in direct sunlight or under a strong tungsten filament lights. Under these kinds of lighting you can see that the amethyst will look a shade darker in color. Under indirect low level sunlight seems to be the best environment to give the amethyst its darkest colors. If the amethyst is sold in direct sunlight it will look much lighter than the same material sold in the shade.
You should not display your amethyst geode in direct sunlight for any length of time. If you desplay it about 6-7 months exposed to direct sunlight it will fade to a pale amethyst color or a gray looking quartz. This eliminates amethyst geodes for outdoor gardening and architectural uses. By displaying it in indirect low level light will make the color last a lifetime.
The good news is?
Amethyst crystals, and geodes have a beautiful color, and the amethyst from Rio Grande do Sul, Brazil is the most brilant in color you are going to find in the mineal world. Everywhere else is going to be less in color, more expensive and or harder to get. Many competitors in the mineral world have their own problems, if only the person you buy them form would tell you these things.
Amethyst geodes are for the most part real tough to break. If you drop one on the concrete from the table height you are likely to end up breaking it in to smaller pieces, but even these smaller pieces have value and can be sold. When you need to clean your amethyst geodes, you can take them outside, hose them off, scrub them with dish soap and your choice of brushes.
