Pyrite Vs. Gold: How to Identify Real Gold from Fool's Gold
Pyrite, often called "fool's gold," and real gold are frequently mistaken for each other due to their similar color and metallic luster. However, they differ significantly in composition, physical properties, and value. Though these substances may appear alike to the untrained eye, several methods exist to distinguish them.
Gold (Au) is a naturally occurring, dense metal that has been prized throughout history for its rarity, beauty, and malleability. It is known for its distinctive yellow luster and ductility.
In contrast, pyrite (FeS₂) is an iron sulfide mineral with a brassy-yellow hue and metallic sheen, similar to gold. Commonly found in sedimentary rocks and mineral deposits, pyrite's abundance often leads to confusion with real gold.
This article will highlight the key differences between pyrite and gold and provide practical methods for accurate identification.
Methods for Identifying Fool’s Gold from Real Gold
Color and Appearance
Pyrite: Has a brass-like or pale to medium brassy yellow color. Over time, pyrite can tarnish, leading to darker colors or an iridescent effect due to oxidation, which can produce hues of brown, black, or even rainbow colors. Pyrite can have a glittery appearance due to its crystalline structure, but it lacks the deep, consistent warmth of gold.
Gold: Exhibits a bright, rich yellow or golden color. Its color is often uniform and doesn’t tarnish or change over time.
How to Test: Visually inspect the color. If the color appears more dull or brassy with tarnish or iridescence, it’s likely pyrite. Gold retains a bright, consistent yellow color.
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| A visual comparison of gold and pyrite. Gold is shown with a deep, rich yellow color, while pyrite appears more brassy and slightly lighter with a metallic sheen. |
Streak Test
Pyrite: When rubbed on an unglazed porcelain tile, pyrite leaves a greenish-black to brownish-black streak.
Gold: Gold leaves a yellow or gold streak when rubbed on the same tile.
How to test it: Rub the mineral across an unglazed ceramic tile (found in hardware stores or mineral kits). The color of the streak will reveal whether it is gold or pyrite.
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A visual comparison of the streak test for pyrite and gold. |
Density and Weight
Pyrite: Much less dense than gold. Pyrite’s specific gravity ranges from 4.9 to 5.2, which means it feels lighter when compared to gold.
Gold is extremely dense, with a specific gravity of 19.3, making it one of the densest naturally occurring elements. Gold feels much heavier than pyrite when held.
How to test it: Pick up both minerals and compare their weights. If one feels much heavier than it looks, it’s likely gold. Pyrite feels lighter in comparison to its volume.
Magnetism
Pyrite: Pyrite is not magnetic but can contain traces of other elements that may make it slightly responsive to magnets.
Gold: Gold is not magnetic, and pure gold will show no magnetic attraction.
How to Test it: Bring a strong magnet close to the mineral. If it is attracted to the magnet (even weakly), it’s not pure gold. Pure gold will not respond to a magnet.
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| Magnet Test: Pure gold is not magnetic; pyrite may show slight magnetism. |
Hardness (Mohs Hardness Scale)
Pyrite: Pyrite is harder than gold, with a Mohs hardness of 6 to 6.5. It can scratch glass and other softer materials.
Gold: Gold is much softer, with a Mohs hardness of 2.5 to 3. Gold can be easily scratched with a copper penny or a knife, which is not possible with pyrite.
How to Test it: Try scratching the mineral with a sharp object like a knife or copper coin. If the mineral is easily scratched, it is likely gold. If it scratches glass or resists being scratched, it is pyrite.
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Hardness Test: Gold is soft and easily scratched; pyrite is hard and scratches glass. |
Malleability
Gold: Gold is malleable, meaning it can be flattened or bent when struck with a hammer or pressed without breaking. This property makes gold easy to shape into jewelry or coins.
Pyrite: Pyrite is brittle and will shatter or break into pieces if struck with force, rather than deforming.
How to Test it: Strike the mineral with a hammer or apply pressure to bend it. Gold will deform but not break, while pyrite will break or crumble.
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Malleability: Gold deforms under pressure; pyrite breaks or shatters. |
Crystal Shapes
Pyrite often forms in perfect cubes, octahedrons, or pyritohedrons due to its cubic crystal system. These crystals can be striated, with lines running parallel on each face.
Gold rarely forms visible crystals in nature but when it does, it's in the isometric system,though it's more commonly found in nugget form or as flakes and grains.
How to inspect it: Observe the shape of the mineral. If it has cubic or octahedral crystals, it’s more likely pyrite. Gold usually appears in irregular or nugget shapes. Also, Gold typically has a smooth texture when pure, while pyrite might show striations or a more crystalline structure on its surface.
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Pyrite forms in well-defined cubic or octahedral crystals. |
Odor Test
Pyrite: When struck or when it reacts with certain chemicals, pyrite can release a sulfurous odor, reminiscent of rotten eggs due to the sulfur content.
Gold has no odor, being chemically inert.
Sound Test
Gold: When dropped on a hard surface Produces a soft, heavy thud. This sound reflects its weight and the way it absorbs the impact rather than reflecting it back as sound.
Pyrite: Being brittle, pyrite can produce a sharper, sometimes even a ringing or clinking sound when dropped. This is because it doesn't absorb the impact as well as gold; instead, the energy can cause a more resonant or sharp noise due to its crystalline structure and lesser density compared to gold.
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| Pyrite can tarnish, often showing iridescence or a darker tarnish. |
Acid Test
Gold is resistant to most acids. However, it can be tested with aqua regia (a mixture of hydrochloric and nitric acid) or other gold testing solutions that react with gold.
Pyrite reacts with acids, particularly hydrochloric acid, producing sulfur dioxide gas and leaving behind a residue of iron sulfate.
Professional Testing Methods
Fire Assay: This is a professional laboratory test where the sample is melted and the gold content is analyzed. This is the most accurate test for determining if a sample contains gold.
Acid Test: This test uses a small amount of nitric acid to determine whether the metal in question is gold or not. Real gold will not react to nitric acid, but pyrite may react and produce bubbles of sulfur dioxide gas.
X-ray Fluorescence (XRF): This method uses X-rays to determine the elemental composition of the sample. XRF can distinguish between gold and other minerals like pyrite based on their atomic makeup.
Electronic Gold Testers: These devices can measure the electrical conductivity of a sample. Pyrite is a semiconductor, which means it can conduct electricity, but not as well as metals like gold. Gold is an excellent conductor of electricity, which is why it's extensively used in electronics, particularly in connectors, switch contacts, and connection strips.
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| Gold on quartz on the left, druzy pyrite on quartz on the right. |
Summary of Key Identification Methods
- Weight Test: Gold is much heavier than pyrite.
- Streak Test: Gold leaves a gold streak, while pyrite leaves a dark green/black streak.
- Hardness Test: Gold is soft and easily scratched; pyrite is hard and scratches glass.
- Malleability: Gold deforms under pressure; pyrite breaks or shatters.
- Crystal Shape: Pyrite often forms cubic or geometric crystals, while gold does not, gold forms nuggets or irregular shapes.
- Luster: Pyrite can appear shinier and more glittery than gold.
- Color and Shine: Gold is a rich, warm yellow. Pyrite is brassy and tarnishes.
- Magnet Test: Pure gold is not magnetic; pyrite may show slight magnetism.
- Acid Test: Gold is resistant to nitric acid; pyrite reacts and produces sulfur dioxide gas.
While pyrite and gold may look similar at first glance, careful examination reveals several key differences. By observing color, luster, hardness, density, streak, magnetism, and crystal structure, one can accurately identify whether a specimen is genuine gold or merely fool’s gold. Utilizing these methods will help avoid costly mistakes and ensure that you can confidently identify and value precious materials.