Pyrite, commonly known as “fool’s gold,” is a mineral that often gets mistaken for the real thing due to its brassy golden color. However, there are several distinctive tests that can reliably distinguish pyrite from gold. Carefully examining characteristics like color, crystal shape, density, hardness, and streak can reveal the difference between pyrite and precious metals like gold.
While pyrite has a pale brass-yellow color, gold has a brighter golden to yellowish hue. Pyrite’s isometric crystal structure tends to form in cubic shapes, while gold is found in irregular nuggets and flakes. When scratched, pyrite leaves a greenish-black streak compared to gold’s golden streak. Gold is also softer, denser and untarnished compared to mineral specimens. An experienced eye can start to notice these subtle differences.
Distinguishing pyrite from other similar minerals like chalcopyrite and marcasite also requires careful observation of color, streak, tarnish patterns, hardness and crystal structure. While identifying these minerals can be challenging at first, gaining hands-on experience with mineral specimens makes it easier to reliably tell them apart. With practice, even inexperienced rockhounds can master the tests necessary to confidently identify fool’s gold pyrite and distinguish it from real gold.
What is Pyrite?
Pyrite is a mineral composed of iron disulfide (FeS2) with a pale brass-yellow color and metallic luster. It crystallizes in the isometric system, often forming cubic, octahedral or pyritohedron shapes. While pyrite has a superficial resemblance to gold, it is much harder and lighter in density.
Pyrite is sometimes referred to as “fool’s gold” due to people mistaking it for real gold throughout history. While pyrite is abundant and inexpensive, gold is a rare precious metal with significant monetary value. That’s why it’s important to be able to reliably identify pyrite and distinguish it from gold or other precious metals.
Visual Identification of Pyrite
The first step in identifying pyrite is through visual inspection of its characteristic physical properties. With practice, you can identify most pyrite using just visual cues. Here are the main things to look for:
Pyrite has a distinctive brass-yellow color, usually a pale yellow with a slightly metallic hue. This pale brass-yellow is a distinctive identifier for pyrite.
Gold, on the other hand, is a deeper and brighter yellow in color, without the subtle brassy overtones. Native gold may also contain silver, giving it a paler whitish-yellow color.
So if you see a metallic pale brass-yellow mineral, it’s likely pyrite. A brighter lemon-yellow color indicates gold instead.
The crystal structure of pyrite tends to form cubes, octahedrons, or pyritohedrons (dodecahedrons with pentagonal faces). Finding cubic, multifaceted crystals is a strong indicator of pyrite.
Gold, on the other hand, usually occurs as irregular nuggets or flakes rather than geometric crystals. The presence of cubic crystals is a good sign it’s pyrite and not gold.
Pyrite has a metallic luster, meaning it looks like polished metal with noticeable reflectiveness and shine. However, pyrite’s luster is not quite as bright and reflective as gold. So a more muted metallic luster suggests pyrite.
Gold has a brilliant golden luster that is very reflective, like a mirror. A brighter, shinier, more reflective luster indicates real gold rather than pyrite.
Pyrite has a Mohs hardness of about 6-6.5, making it a relatively hard mineral. It cannot be easily scratched with a knife or fingernail. Gold, on the other hand, is much softer with a Mohs hardness of just 2.5-3.
So you can distinguish pyrite from gold by trying to scrape or scratch the mineral. If it easily bends, dents, or scratches, it’s gold. If it strongly resists and remains intact, it’s likely pyrite.
Physical Property Tests
Beyond visual inspection, you can identify pyrite through hands-on testing of its physical properties like streak, density, conductivity, and magnetism.
The Streak Test
One of the quickest identification methods is the streak test. Take your mineral sample and drag it across a piece of unglazed ceramic. This will produce a “streak” of fine powder that reveals the mineral’s true color.
Pyrite has a greenish-black streak color. Gold, meanwhile, has a golden yellow streak. So streak testing can instantly reveal pyrite even if the sample visually appears golden.
Density and Weight
Gold is much denser than pyrite, with a specific gravity around 19.3 compared to just 4.9-5.0 for pyrite. That means a gold nugget will feel significantly heavier than a similarly-sized pyrite sample.
You can conduct a simple density test by weighing your mineral on a precision scale. The density ratio will help indicate whether it’s pyrite or denser gold. Gold also feels heavier in the hand compared to pyrite.
Iron is a key element in pyrite. But unlike other iron minerals, pyrite is not magnetic. This makes a magnetism test helpful for identification.
Take a strong neodymium magnet and bring it close to your mineral sample. If it attracts, then it is likely magnetite or another magnetic mineral. No attraction means it could be pyrite or gold.
Pyrite is conductive to electricity while gold serves as an electrical conductor. You can test conductivity by touching wires from a battery to the mineral. Sparks indicate pyrite while no reaction suggests gold.
This conductivity demo can be done during science lessons and mineral identification courses to showcase pyrite’s special properties. Just take proper safety precautions when working with electrical circuits.
Advanced Identification Methods
Chemical testing and specialized lab techniques can also definitively identify pyrite and distinguish it from other minerals. Here are a few advanced identification tests:
When struck forcefully with a metal object, pyrite gives off a distinctive sulfur smell, similar to rotten eggs. This sulfur scent provides a quick way to identify pyrite samples.
Applying nitric acid to pyrite produces a distinctive blue-green reaction, thanks to the sulfur in pyrite. No reaction occurs with metals like gold. So fizzing and color changes reveals the presence of pyrite.
Special techniques like mass spectrometry and energy-dispersive X-ray spectroscopy can detect pyrite’s unique chemical signature. Spectroscopy provides the most definitive identification of pyrite short of visual confirmation of its crystal structure.
Distinguishing Pyrite from Other Minerals
Fool’s gold pyrite has many lookalikes. There are a few other golden minerals that can be easily mistaken for pyrite. Here’s how to distinguish it from some common pyrite imposters:
Chalcopyrite is a brassy yellow mineral made of copper iron sulfide (CuFeS2). It has a deeper yellow hue than pyrite’s pale brass color, although the two can appear similar.
Pyrite is harder than chalcopyrite, with Mohs hardnesses of 6-6.5 vs 3.5-4. And pyrite leaves a greenish-black streak, while chalcopyrite’s streak is more bluish-green. Chalcopyrite also shatters under force while pyrite is sturdier.
So hardness, streak, and tenacity tests can separate the two. Chalcopyrite also tarnishes differently than pyrite.
Marcasite is a lighter yellow-whitish mineral that forms in thin tabular crystals instead of pyrite’s cubes. It has the same chemical composition but a different structure than pyrite.
Marcasite also degrades faster when exposed to air. So distinguished crystal shape and signs of weathering identify marcasite vs pyrite.
Arsenopyrite contains arsenic rather than the iron present in pyrite. It has a silver-white color that distinguishes it from brassy pyrite. Hardness and streak tests can also identify arsenopyrite.
Bornite is an important copper ore with an iridescent tarnish. Its purple, blue, and red hues differ from pyrite’s blackish, greenish, or bluish tarnish colors. Bornite is also much softer than pyrite.
Pyrrhotite is an iron sulfide mineral with a bronze color that ranges from yellowish to grayish. Its structure is monoclinic rather than the isometric crystal system of pyrite. It is also magnetic, unlike pyrite.
Comparison Table of Pyrite and Some Minerals It Is Commonly Confused with
|Mineral||Color||Luster||Hardness||Streak||Crystal System||Density||Magnetism||Other Distinguishing Traits|
|Pyrite||Pale brass-yellow||Metallic||6-6.5||Greenish-black||Isometric||4.9-5.0||Non-magnetic||Brittle, cubic crystals, sulphur odor when struck|
|Gold||Golden yellow||Brilliant metallic||2.5-3||Golden yellow||Cubic (rarely forms crystals)||15-19||Non-magnetic||Very dense, malleable, ductile|
|Chalcopyrite||Brassy yellow||Metallic (iridescent tarnish)||3.5-4||Greenish-black to bluish-green||Tetragonal||4.1-4.3||Non-magnetic||Brittle, weathers rapidly|
|Marcasite||Pale yellowish||Metallic||6-6.5||Greenish-black||Orthorhombic||4.4-4.7||Non-magnetic||Tabular crystals, fragile, discolors in air|
|Arsenopyrite||Silver-white||Metallic||5.5-6||Dark grey to black||Monoclinic||6.2||Non-magnetic||Contains arsenic|
|Bornite||Purplish-brown||Metallic||3||Greyish black||Orthorhombic||4.9-5.1||Non-magnetic||iridescent tarnish colors|
|Pyrrhotite||Bronze yellow to grayish||Metallic||4-4.5||Greyish black||Monoclinic||4.5-4.7||Magnetic||Contains less iron than pyrite|
When in Doubt, Ask an Expert
If you come across a tricky mineral specimen that you can’t confidently identify, don’t be afraid to ask for help. Consult a geologist, mineralogist, lapidary, or rockhounding expert. There are also great mineral identification resources online that can aid in identification.
With enough first-hand experience, you will start noticing the subtle differences between pyrite, gold, and other minerals. But handling real mineral specimens is the best teacher. Consider starting a reference collection with samples of pyrite, gold, chalcopyrite, and other commonly confused minerals. Learn their properties through hands-on testing and inspection.
Frequently Asked Questions about Identifying Pyrite
How can I tell pyrite apart from gold?
Pyrite and gold can look similar, but pyrite has a pale brass-yellow color while gold is a richer golden yellow. Pyrite also forms in cubic crystals unlike gold’s irregular nuggets. Pyrite is harder than gold, with a metallic luster that’s less reflective than gold’s brilliance. Scratch tests and density comparisons can also distinguish pyrite from gold.
What’s the best way to identify pyrite?
The streak test is one of the quickest ways to identify pyrite. When scratched on ceramic, pyrite leaves behind a greenish-black streak. Gold leaves a golden yellow streak instead. Streak testing combined with visual inspection of color, luster and crystal habit make pyrite easy to identify.
Why is pyrite called “fool’s gold”?
Pyrite earned the nickname “fool’s gold” because its pale golden hue tricked many inexperienced prospectors into thinking they’d struck it rich. Pyrite’s superficial resemblance to gold fooled people throughout history, until tests like streak, hardness and density were developed.
How can I tell the difference between pyrite and chalcopyrite?
Chalcopyrite has a brighter, more golden yellow color than pyrite’s pale brass hue. It also leaves behind a greenish black streak with hints of blue rather than pyrite’s darker streak. Chalcopyrite tends to be softer and tarnishes differently than pyrite. Hardness and streak tests are the best ways to distinguish them.
Is pyrite magnetic?
No, pyrite is not magnetic, unlike some other iron sulfide minerals. This makes a magnetism test helpful for identification. Moving a strong magnet near pyrite will not produce any attraction. Magnetite and pyrrhotite are magnetic minerals sometimes confused with pyrite.
What should I do if I can’t identify a mineral sample?
If you can’t determine whether a mineral is pyrite or something else, consult an expert. Geologists, mineralogists, and lapidarists can often identify mystery mineral samples. There are also great online mineral identification resources and communities that can help provide an ID.
Where can I find pyrite specimens to practice identifying?
Pyrite is very common and inexpensive to acquire. Check local rock shops, science stores, museums, college geology labs or online mineral dealers to find pyrite samples. Having real mineral specimens to test and handle is the best way to master pyrite identification.
Identifying pyrite takes patience and practice but anyone can master it. By getting to know pyrite’s distinctive visual features, physical properties, and chemical qualities, you’ll be able to reliably distinguish this classic “fool’s gold” from real gold and other minerals. Just remember to inspect color, luster, crystal shapes, hardness, density, and streak. Conduct multiple tests when unsure. And don’t be afraid to ask more experienced mineral experts for assistance. Follow these best practices for identifying pyrite and you’ll be able to spot it every time!