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Tuesday, August 13 2019

The type of stones you use for rock tumbling is largely personal preference. But whether you collectrock tumbler them on your own or buy rough stones, for best results stick to stones of similar hardness but of various sizes when tumbling together. This will ensure they all take approximately the same amount of time to reach the proper smoothness, and that harder stones don't damage softer stones during the tumbling process. 

Many types of rock can be successfully polished into stunning gems, especially agates, quartz, and jasper. Agate is the most popular tumbling rough. It is generally inexpensive and can be tumbled with good results by beginners. Agate occurs in a wide range of colors which include: brown, white, red, gray, pink, black and yellow. The colors are caused by impurities and occur as alternating bands within the agate, providing interesting and pretty patterns.

Any rock with a hardness of 5-7 on the Mohs hardness scale will generally take a nice polish in a rock tumbler. Agates have a hardness of 7. Harder rocks usually result in a high-gloss finish. Softer rocks will get smooth and rounded, but they won't take a polish. If the rock looks earthy, it will generally still look earthy when you take it out of the tumbler. Mohs Hardness Scale is named after its inventor, Friedrich Mohs, a German mineralogist. The scale was developed in 1812. He selected 10 mineralMohs Hardness Scales of distinctly different hardness (hardness is the resistance of a material to being scratched) that ranged from a very soft mineral (talc) to a very hard mineral (diamond). Since you always want to tumble together stones of similar hardness for best results, it's important to understand this principle.

The key point to remember in collecting or purchasing rough material for your tumbler is: "quality in means quality out!" Don't waste time and money on grits trying to smooth out crevices and holes in a poor rock. Start out right by only using the type of rocks that are known to provide the best results when polished.

To start, fill the rock tumbler barrel between 2/3 and 3/4 full. Choose rocks of varying sizes, as this will promote thorough tumbling action. A batch of rocks that are all about the same size will often not tumble properly or grind very slowly. For a 3 pound barrel, a good range of sizes is from .25 inch to 1.5 inches. Lortone Rock Tumblers found here.

If you don't happen to live where agates can be found in stream beds or where quartz pebbles can be found along beaches, that's OK.  You can still enjoy tumbling rocks by purchasing the rough materials online. Although it's fun to collect your own rocks, it is often much more economical to purchase them. And remember that collecting on private property without permission is unlawful and that removing rocks from parks and most other types of public land is also illegal.

Rocks NOT to Tumble

It's just as important to know what type of rocks you should NOT tumble, as it is to know which ones with produce nice round and shiny gemstones. Sedimentary rocks such as sandstone, coal, limestone and shale are too soft or poorly cemented to polish into shiny gems. Metamorphic rocks that contain micas or have a "grainy" texture are also unsuitable - they will break up instead of becoming smooth. And, most igneous rocks do not tumble well because they contain several different minerals that wear down at very different rates.

Nugget of News Blog

Posted by: Denise AT 02:21 pm   |  Permalink   |  Email
Sunday, July 14 2019

Alluvial gold refers to tiny gold flakes that come to be through water erosion and movement. In geology, alluvium alluvial goldis loose sediment which has been eroded from a primary source, transported and further eroded by water, and redeposited. Since gold is extremely dense, it is easily trapped alongside other dense alluvial particles. The bits of gold found in these deposits of alluvium are called “alluvial gold.”

The alluvial environment is a very complex one, with many natural forces competing with each other. The forces that lay down gold are a summation of many flood water events of varying intensity that cause the reworking of sands and gravels. Between major flood events, water naturally flows along the already created path and typically the gold present in the gravel or on the surface will not move much. But the larger flooding events can change the drainage routes and even the river’s shape. Some curves can be shut off from the stream and bypassed.  Where the water speed decreases, gravels will drop out of suspension, creating alluvial pay streaks that are typically located along and near the riverbed.

To identify where a pay streak might be located, take the flow of the waterway into consideration. The most productive streaks are formed as a result of major floods that are significant in terms of both water flow and intensity of erosion. Greater amounts of gold are present here as compared to regular gravels. Pay streaks tend to possess a comet-like form. At the “head” or “heart”  is found the richest concentration of gold. At this location, the gravel is coarser and the sandy and silty fraction is much less. This little bit of silt is present only for a few centimeters on the surface, laid down in the last phases of the flood as the silt is dropped. The gold in these gravels is typically small flat flakes, with maybe a small picker or two.

As gold prospectors, our objective is to learn to read a stream and recognize the pay streaks it contains. Think about where you are going to dig before you start and then repeatedly test the gravel you are processing. It is important to consider the presence, form, and depth of the bedrock on which the water and all the alluvial gravel deposits are sitting. In many cases, the gold will naturally concentrate in the lowest part of the riverbed, making a gold-rich path. During high water events, much of the gold is picked up and put back into motion, which leads to forming new pay streaks. Some will be laid back down along the low line of the stream, but may also end up a little farther downstream. The gravels in contact with the bedrock or false bedrock base are often the richest. The same facts apply to the alluvial pay streaks that are formed on gravel bars— the lowest level of the gold-bearing gravel is normally the richest.

The alluvial environment changes over time. Alluvial pay streaks generated 100 years ago could become buried, then subsequently be eroded and exposed again. The erosion might be in part or in total, generating a new series of paystreaks further downstream. Pay particular attention to large boulders and trees. Obstacles like these may partially block the water flow and provide an opportunity for increased gold concentrations, especially behind the obstructions. If there are fissures, holes or natural traps in the stream, be sure to sample these areas, too.

Although high water events are sporadic, when you do find a paystreak caused by one, it can be a very productive spot. Stick with it and keep in mind most are small and narrow and best worked by hand with a sluice and gold pans. 

Nugget of News Blog

Posted by: Denise AT 08:09 am   |  Permalink   |  Email
 

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