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Why Do Common Fossils Come In Different Colors?

When it comes to the most common fossils available in the market for collectors to buy, the basic process of its fossilization involves mineral replacement as remains, such as bones, are buried in the ground. Buried bones absorb minerals from groundwater, filling in microscopic gaps. The organic, or original, material in the bone degrades over time, while minerals fill in the empty spaces where the organic material once existed. Finally, the bone contains little, if any, organic material and is primarily composed of hardened minerals. As a result, the bone's weight increases dramatically, and its color changes to match the replaced minerals.

Different Minerals Produce Different Colors

Minerals and Fossils come in a wide variety of colors. Examples include phosphate, a mineral commonly used to replace shark teeth. Phosphate is a jet-black mineral. If phosphate replaces the original material, the fossil will become black. Iron-rich areas produce red and orange-colored fossils. Areas with gray clays and limestone will also produce a gray-green or gray-yellow color, similar to shark teeth found in North Carolina.


It is more complicated than the simple explanations above. There are additional nuances to consider, including original material density, pressure, heat, chemical reactions, time buried, saturation, acidity, and more. For example, shark teeth have a very dense dentine crown and a very porous root. As a result, fewer minerals will replace the material in the crown compared to the root. This uneven mineral replacement will result in a difference in color and hardness between the shark tooth root and crown.

Another example of complications is the length of time fossils have been buried. Over millions of years, many different minerals can seep into and out of fossils, imparting different colors. White plant fossils on black shales discovered in central Pennsylvania and parts of Germany provide an interesting example of multiple mineral replacements. These plants sank into oxygen-depleted waters and were quickly buried by fine gray sediment.

The plant-filled sediments eventually subducted deep underground, where heat and pressure cooked the plants, resulting in an ash-like black carbon film. Pyrite in the ground replaced the carbon film, resulting in orange plant fossils. However, through oxidation and replacement reactions, the pyrite was eventually replaced by a white substance known as pyrophyllite, causing many of the orange fossils to become white. These beautiful white fossils can still be found today in black shale deposits.

Streaks or "lightning" patterns can appear on fossils. This is caused by fossils resting on another underground object, such as pebbles or roots. Tiny tree roots growing against the fossil will leach minerals, lightening the color. When the fossil erodes, the tiny tree roots fall off, leaving small lightning patterns.

Actual Colors Can Sometimes Be Preserved

A fossil may contain a small amount of its original material. This organic material becomes trapped between the minerals. Typically, these organic patches are only microscopic bits, but with today's advanced techniques, such as electron microscopes and ion mass spectroscopy, paleontologists can study the chemical traces left by these minute amounts of original material and deduce all kinds of information of some of the most popular dinosaurs, including their color. Using these modern techniques, paleontologists can deduce the animal's colors and color patterns from well-preserved feathers and skin, which contain melanosomes with preserved pigmentation.

Mosasaur and dinosaur feathers are excellent examples of color preservation. A mosasaur's well-preserved skin patches reveal that it had dark pigmentation. This means that mosasaurs were dark gray or black, similar to sperm whales.

A few dinosaur color schemes have also been identified through some of the most complete dinosaur fossils. Pigments found in the feathers of theropod Sinosauropteryx indicate that it had orange feathers and a striped tail. The dinosaur Anchiornis Huxleyi had a mostly black body with white accents, a dark orange headdress, and freckles on its head.


The most common fossils in the market come in a variety of colors, which are caused by the complicated mineralization process rather than the organism's original color. Some colors and patterns are highly sought after by collectors, increasing the value of a fossil. A mottled red shark tooth from the "Fire Zone" in Bakersfield will be far more valuable than a similar jet-black tooth from South Carolina. When you have time, examine the colors of your fossils and imagine the various processes they underwent.

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