- Scratch your ore against an unglazed white ceramic streak plate. If it's gold, it will leave a golden streak.
- Or, scratch the surface of the specimen with a knife. Gold is a soft metal that will show scratch marks.
- Raw gold forms in veins of granite, quartz, iron ore, or sulfide. It's brassy yellow, glows in light, and can be scratched with a fingernail.
Field Tests for Identifying Gold Ore
Streak test Scratch the mineral against an unglazed white ceramic streak plate. Gold will leave a gold residue, while minerals like pyrite and mica will leave black and white streaks, respectively. This test will damage your sample.
Scratch test Gold is a very soft element, so scratching it will leave marks. Use a knife to try and scratch the surface of your rock. If it’s gold, you’ll see scratches. Pyrite will be too hard to be affected, and mica will flake off when scratched. If you don’t have a knife handy, scratch gold with a piece of copper (like a penny). Pyrite, on the other hand, will scratch the copper. This test will also damage your sample.
Impact test If you have a large specimen, hit it with a hammer. Pyrite will shoot out sparks, while gold will flatten under the pressure. Mica will fall apart when struck. When gold has a crystalline structure, it’s even more valuable. An impact test can greatly damage your gold’s structure.
Smell test Give your sample a good rub down with the pad of your finger, then take a whiff. Gold is odorless, but sulfur rich pyrite smells like rotten eggs. This test doesn’t hurt your gold, but it also can’t distinguish gold from mica, which is odorless.
Magnet test Pyrite is magnetic and gold isn’t. If you place a magnet against the rock and it sticks, it’s at least mostly not gold. Gold does, however, form near pyrite sometimes, so there could be trace amounts of gold in your sample. Mica isn’t magnetic either, so be sure to conduct more than one test on your rocks. This test won’t hurt your sample.
Gold detector test Check for gold using a gold detector, the same way you’d find other metals with a metal detector. They use low frequency magnetic fields or pulsing magnetic fields to determine whether the metal beneath them is gold or not. Because nothing’s touching your sample, this test won’t damage it at all.
Lab Tests to Identify Gold Ore
Panning Gold is very heavy (19.28 g per cubic centimeter, or .7 lbs per cubic inch). That means if you crush your sample in tiny pieces, the gold will collect at the bottom. Pan the gold by putting the crushed material into a pan and swirling water in it. As the less dense materials flow off the top, you’ll be left with gold in the bottom. This is a good way to test for flakes of fool’s gold, which will float on the water.
Acid testing Check a rock for gold by dissolving the surrounding material in an acid. The safest way to do this at home is to use white vinegar. Simply put the rock in a glass container and completely cover it with vinegar. Let it sit until the rock dissolves, and you’ll only be left with gold. This test won’t always work, however, since the acid is weak. Stronger acids will produce foam when they come in contact with other materials, but not gold.
Break testing If you suspect there’s gold embedded in the rock that you can’t see, break it open and examine the interior. Use a rock saw or hammer to open the rock. Rock saws are considerably more expensive than hammers, but the clean edge will make it easier to identify free gold in the rock.
Weight testing If you know what material you’re working with—granite, iron, quartz—weigh a piece of a similar size against your sample. If the sample is significantly heavier, it could contain gold. This is an inexact way to check for gold. The absolute best way to determine if you have gold ore or not is to hire an assayer who will analyze the mineral contents of the rock.
Visual Properties of Gold Ore
Gold is brassy yellow. There are many minerals out there that look like gold in it’s best known form—shiny, pure, processed gold. Gold in ore, however, isn’t as golden as you may expect. Instead, look for brassy yellow veins, flecks, and clumps. You won’t always be able to tell if gold is present based on looks—it could be entirely embedded within the rock.
Gold shines when shaded. Gold is highly reflective, so it doesn’t need a lot of light to produce a shine. Take your sample into the sunlight, then cover it with your hand. If it’s gold, it’ll shine even in the shadow. Gold will not, however, reflect light like a mirror. Fools gold and other gold-like objects will flash light right back at you, while gold will produce more of a glow.
Gold has smooth edges. If you’ve found a gold nugget, it’ll have smoothed out sides. Gold is very soft, so as it tumbles through streams and other particulates, its edges get worn down. There are other minerals that have this property too, however, so check for color and shine as well.
Gold doesn’t tarnish. Gold jewelry can tarnish, but not native, or pure, gold. If your sample has any rust or discoloration, it’s likely to be pyrite or another mineral.
Gold has no striations. Striations, or thin parallel lines that form on the face of minerals, are present in pyrite but not gold. Gold can, however, occasionally form in a crystal structure, which can be mistaken for striation.
Kinds of Gold Ore
Placer gold When you’re panning for loose gold in gravel and sand, you’re looking for placer gold. Placer gold is already separated from the rock it formed in and can look like flakes, powder, or nuggets. For flakes and powder it’s best to assay the gold with an acid or heat test. Gold nuggets, however, will look like rounded yellow stones.
Lode gold This is the gold that is still in the rock. Lode gold is found in quartz veins, with other precious metals in igneous and metamorphic rocks, and with iron ore in sedimentary rocks. There are several types of lode gold ore: Quartz gold ore is found in large veins of quartz, most commonly rose quartz and rainbow quartz. If the gold is on the surface of the rock it’ll look like shiny yellow flecks or veins of gold. Iron oxide copper gold ore is found on the edges of granite or as long bands of dark rock flecked with gold. Sulfide gold ores will be filled with shiny flecks, but not all of them will be gold. Gold and fool’s gold can form alongside each other, making this kind of ore deceptively chock full of shiny material. Blue clay gold ore is found in, you guessed it, blue clay. It will be mixed up with black sand and tiny pieces of quartz. Granite gold ore looks like flecks of gold in the dark parts of granite.
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