Alluvial amethyst

alluvial amethyst Amethyst is dichroic, showing a bluish or reddish purple tinge when viewed from different angles. Much amethyst that is mined is heat-treated to change the color to yellow -- which explains much of the citrine on the market today, natural citrine being somewhat rare. amethyst mine, brazil photo:silvestre garimpo One of the world's major producers of natural amethyst is the Anahi Mine in Bolivia (which also produces ametrine). The mine is located in the midst of the rain forest zone near the Pantanal wetlands, which establishes the borderline between Bolivia and Brazil. Accessible primarily by bush plane, the mine is four hundred kilometers east and slightly south of Santa Cruz, Bolivia. In Brazil and Uruguay, amethyst is often found in alluvial deposits in the beds or former beds of rivers where miners use the techniques of placer mining. (Alluvial gems often have quite a high specific gravity [density] compared to other minerals so that they are easily trapped in depressions in stream beds. This causes them to become concentrated, making them easier to mine.)

Geodes are a variable phenomenonand, therefore, many theories exist toexplain how they are created. The term geode is derived from the Greek word geoides which means "earthlike."  Some geodes are completely filledwith small compact crystal formationssuch as agate, jasper or chalcedony and are called nodules. The only differencebetween a geode and a nodule is that a geode has a hollow cavity, and a nodule is solid.  Volcanic lavas such as basalts may have round or almond shaped gas holes, partially or completely filled withcalcite, chalcedony, agate, crystallized colorless or amethyst quartz or other minerals. Many easily accessible geode collecting sites exist in the western US -- including California, Arizona, Utah andNevada. The state of Iowa is also hasgeodes: in fact, they are so prevalent thegeode is Iowa's state rock. A relatively cheap stone because it is aquartz, amethyst is found throughout the world. Were amethyst not so plentiful it would be much more expensive, given its beautiful range of purple shades, ranging from deep purple to lilac to mauve to purplish reds. If, after creating citrine from amethyst, one decides amethyst would be more desirable, the pseudo-citrine can bechanged back to the original amethystcolor by subjecting it to X-ray radiation. Methods of accessing alluvial gem gravels include open pits, shafts and tunnels, and dredging.

geodes: the variable phenomenon One of the amethyst forms with which the public is most familiar is the geode, split into two halves. what is a geode? amethyst geode Geodes are hollow, crystal-lined globular rock cavities lined with crystals that are found in sedimentary rocks like limestone (calcium carbonate) and dolomite (calcium magnesium carbonate) or in volcanic rocks. how are geodes created?Beginning as bubbles in volcanic rock or as animal burrows, balls of mud or tree roots in sedimentary rock, over a period of millions of years the outer layers of silica cool and harden while at the same time water containing dissolved silica begins to seep into the lava cracks or cavities. Eventually, the deposited silica minerals create crystals, most of which point towards the center of the cavity. Each geode is unique -- its secrets can only be discovered by cracking it open or dissecting it with a rock saw. The size and formation of crystals and their different shades of color is what makes each geode special, as a geode's rough exterior gives no indication of the often breath-taking secrets held within. For those who collect geodes, the anticipation of finding out what's inside never fades.