Look, there really is “rich gold” in the fossils!

In many stone exhibitions or natural science museums, you will see a kind of golden biological fossils. They are beautiful and magical, like pieces of "handicrafts" cast in brass and carefully carved. They are so beautiful that people even doubt that they are not natural products.

Common fossils are mostly stones with similar composition to various rocks, such as calcium, silica, and carbonaceous. In addition, there are various ways to fake fossils, so this suspicion is not without reason.

In fact, this type of fossil is not man-made, but a rare pyrite fossil. Logically speaking, pyrite is not a particularly rare mineral, and there are many fossils formed by organisms, so this type of fossil should be rare. Why is it so rare? This starts with their formation.

The rock strata that formed these fossils are all unoxidized sedimentary rock strata in black, gray or dark green colors, containing organic matter such as asphaltene and carbon. Just like the wells and ponds we are familiar with, due to the formation of an oxygen-deficient microecological environment, smelly and black silt often accumulates at the bottom. These colors are the iconic colors of the restored environment.

The iron element that forms pyrite is commonly found in the mud at the bottom of the sea and lake. When organisms die, the organisms decay and decompose to produce hydrogen sulfide, which reacts with the iron element in the mud to form ferrous sulfide, which is pyrite.

At the same time as pyrite is formed, the replacement reaction with the calcium hard body of the organism that forms the fossil has already begun. The result of this molecular-level replacement reaction is that the delicate structure of the biological fossil is accurately replicated by pyrite, so the details of the fossil are clearly visible.

Pyrite is easily decomposed to form stable limonite when exposed to air, and often forms an illusion of pyrite. Therefore, pyritized fossils with a golden appearance can only be found in very rare environments, such as newly excavated pits deep underground, or when blasting mountains and mining coal. Many of these fossils have already formed limonite-illusion fossils before people have mined and discovered them. Therefore, fresh pyritized fossils are rare.

Since it is rare, it is inevitable that some people will have crooked ideas. However, there is basically no need to worry about counterfeiting of pyritized fossils. Firstly, the pyritization process is quite long. Secondly, the hardness of this mineral is as high as 6-6.5. It is hard and brittle in nature, and it is quite difficult to counterfeit. Even if it succeeds, the cost may be higher than the price of the real thing, which is really not worth it.

Such rare fossils are natural masterpieces with great ornamental value, among which pyritized hornstones, ammonites, trilobites and brachiopods are the most ornamental. Studying them will help people restore and recreate ancient climate, ancient geography and ancient environment, and will be more conducive to the search for sedimentary minerals such as oil, natural gas and coal gas. Therefore, pyritized biological fossils with high ornamental and scientific value are rare collections worth collecting and passing down.

The above is what I shared today. See you next time if you are interested.

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