Ways to Test Gold Ore in the Field
Brass shines as fair to the ignorant as gold to the goldsmiths.
- Elizabeth 1
Gold is very heavy. If you have a piece of rock that seems heavy when compared to its volume and there is evidence of a golden yellow color within, you may have gold. Gold is very soft and can be scratched easily. Using your fingernail or a hard implement, you can sometimes dent the surface.
Field Tests to Determine Mineral Type
Gold ore combines with few elements. Because of this, it is found in nature in pure form, and to a limited extent in gold ores. The gold ores that exist produce a relatively small percentage of all discovered gold. Nagyagite, calaverite, sylvanite, and krennerite are four examples of low-yield gold ore. Since gold forms few compounds, gold ore is relatively rare. Learn about luster, streak, hardness, and cleavage, all of which are physical characteristics that may help identify gold ore prospects.
Streak and Hardness Testing in the Field
Mohs Hardness Testing for Minerals
Let's get down to the nitty-gritty—why learn about luster, streak, hardness, and cleavage? If you are reading this article, you more than likely have an interest in learning about and/or finding gold. I do too.
So if you stumble upon an abandoned mine or start to take a miner's pick to a piece of rock with quartz streaks in it, how do you know (or have good reason to believe) the ore you have attained is a classic gold ore? You can use Mohs tests in the field to determine the ore characteristics and see if that jives with what the Mohs test has to say about gold ore. Though rather rare, gold does appear in forms other than pure nugget or string. It can be mixed in with the minerals calaverite, kennerite, and silverite.
On the Mohs scale, calaverite has a hardness of 2.5 to 3. Cleavage is absent. Its luster is bright metallic. Its color is silver-white to brass-yellow, and its streak is yellow-gray. Using various tools and minerals of known hardness, one can perform a scratch test. The first object or mineral to scratch the ore gives an approximate value for hardness.
Scratching repeatedly over a white glazed tile with a pocket knife gives a measure of powder. When smeared, if it is calaverite, the streak should be yellow-gray. In this manner, many tests can be performed that will give the prospector a better idea of what ore he has discovered.
Carrying a handbook to help you identify minerals is also a good idea. The Handbook of Rocks, Minerals, & Gemstones by Walter Schumann Dr. and R. Bradshaw is reasonably priced and thorough.
Useful Information About Gold Prospecting
- There is a lot to know when starting the hobby of gold prospecting.
- The prospective gold prospector needs to understand the tools involved in gold prospecting.
- One needs to understand how gold placer (alluvial gold) winds up where it is.
- One needs to know about hard-rock mining.
- One needs to figure out where to go on a claim for the first time.
- One needs to know where gold has been found historically.
- One needs to understand his or her state laws and the federal mining laws regarding an individual recreational prospector.
- State geologic survey sites are a good source of information about gold mining. The U.S. Geologic Survey has maps of large gold mining areas.
Testing for Gold Using Streak Plates
Streak plates are glazed white tiles upon which portions of mineral can be scratched off to produce a line of powder. The powdered mineral can then be seen clearly, and the color of its streak can be observed. The streak contrasts with the white quite vividly.
Rubbing a piece of gold across white unglazed porcelain tile will not leave a dark streak. If the streak is black it is not gold. Such a steak could indicate pyrite. Gold will reveal itself as a golden yellow.
If you know you have a piece of gold, hold a magnet near it. If the piece is attracted, there are other metals causing the attraction. Pure gold is not magnetic. If you have a sample you believe is gold and it is not magnetic, it proves nothing. Copper, brass, and stainless steel are not magnetic, for example.
I have found hand lenses for as little as $5. These loupes are 30 power, while some even have LED lights in them. They are lightweight and small, fitting comfortably in the pocket. Many are made with silver-colored metal frames, but reflection of light off of these may interfere with identification. Others are black and made of plastic.
Since all (as far as I know) extraction methods involve chemicals that can produce noxious and deadly gas vapors, there are articles that lay out the procedures. Simply google "gold extraction". Remember to always wear a mask/ventilator if you wish to separate gold from ore (in its pure form) chemically. The building should also have good ventilation. Deferring to professionals when using chemicals may be the right decision.
Of Interest to Gold Prospectors
Finding gold may not be as simple as seeing a gold stringer in a quartz outcropping. Sometimes gold is mixed in ore with manganese. Other times, it can be found in reddish rock, occurring due to iron oxide (rust), with lines of quartz. Another form of volcanic rock, basalt, can contain gold and quartz and varies from a dark black to grey. Yet other times it is in the form of placer, flakes that have washed down a mountain in some kind of water pathway. To increase your yield, you really need to get some basic equipment.
Hobart M. King, PHD, RPG, The Most Important Gold Prospecting Tools, 2005 - -2018, Geoscience News and Information.
Harold Kirkemo, USGS, 2016, Prospecting for Gold in the United States.
Jay Motes, In What Rock Formations Can Gold Be Found?, April 24, 2017.
Staff, How To Test Gold, 2017 Prospecting.com.
Staff, Gold Prospecting for Beginners, 2017.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
Questions & Answers
I think I found a piece of gold. Where can I get it tested?
The best thing to do is go to a certified jeweler. I have had gold tested with chemicals for free. You can also try to find a precious metal consultant. I go to a reputable pawn broker I have used for years. Most simple tests eliminate the possibility of other metals. At that point, you take your sample to an authority on gold.Helpful 16
I live in the Sonoma volcanic and basalt. The soil and rocks have nuggets that are red to yellowish-orange. There are red bands that go between and some nuggets have an orangish color. But they do not look like shiny gold; they produce shine. Can real gold look confusing when it's shine is not golden looking?
In my experience, there is little question about what is gold. As you say, it is yellow and golden. If the gold is dirty/covered with dust you probably cannot even see that it is gold, hence the washing process. I would take a sample to a mining store. Better yet, perhaps you could take it to a college or university nearby and show it to a geologist. They frequently will help with such questions. Orange color may indicate sulfides?Helpful 5
How can l test gold dust? It’s from a stream in the San Bernardino Mountains from a large amount of black sands. It looks like gold in the pan but there’s a lot of pyrites also. It glitters in every ground sample, it’s everywhere. Acid tests don’t affect any of it. They have also separated out from black sands with a magnet. I want to determine if any part is gold.
I understand your problem. Oat gold is hard to differentiate from mica and pyrite because it is so small. However, under a very bright high-intensity light, it shows up as yellow and it glows. Pyrite is burnished and mica is usually shiny only on one side. If you flip it by blowing with a suction tweezer, it is dark. If you need more verification, I would go to a prospecting shop or possibly an assayer.Helpful 1
© 2013 John R Wilsdon