Many fossil eggs and turtle shells are reported in Kentucky. None (so far) have turned out to be fossil eggs or turtle shells. Although it is possible that fossil eggs and turtle shells will someday be found in Kentucky, all of the misidentified fossils that have been reported are actually concretions or man-made objects.

Rock Concretions or rocks rounded by erosion and weathering.

Concretions are not fossils, but sometimes are confused with fossil eggs, turtle shells, and other bones.

Concretions are naturally occurring circular to oval-shaped mineral deposits in rock. Concretions form when mineral layers grow or “accrete” around an organic or mineral particle in sediment. If minerals fill a burrow or void in the sediment, growth will generally conform to the shape of the mineral or void. Some of the resulting rock shapes are called "concretions" or "nodules." In other cases, growth is relatively unconfined and mineral layering expands outward from the original particle (numbered 1 to 4 in the figure) in concentric layers to form concretionary layers around the particle. The layers may be globular (circular in three dimensions) or elliptical with their long axis parallel to bedding. Increased burial pressures (pressing downward) generally compact globular shapes into elliptical shapes. With time, both the mineral layers and surrounding sediment are turned to stone.

Concretions form through growth of mineral layers around a particle.
Concretions form through growth of mineral layers around a particle.

Concretions occur in many Kentucky rock layers. They can be smooth, grainy or textured similar to the surrounding rock layers, or cracked into polygonal patters. Cracking patterns may give the concretions the crude appearance of cracked eggs or turtle shells.

Concretions form in many different rock layers, with many different types of minerals, with many different colors and textures. Carbonate and quartz concretions occur in many of Kentucky’s limestone units. They are also common in some shale units. In Pennsylvanian strata of the Eastern and Western Kentucky Coal Fields, large carbonate concretions more than five feet in diameter occur in dark gray shales.

Siderite is another type of mineral that forms concretions. It is common throughout Kentucky. Generally siderite forms red, orange, or brown concretions, from inches to a foot in length. Some siderite concretions are oval to circular or globular in shape. Some area irregular in shape, and are more commonly called “nodules.” Siderite concretions and nodules sometimes fill the voids left by burrowing organisms, called trace fossils.

Quartz (silica) is a very common concretion-forming mineral. If the circular to oval rock is solid quartz throughout, it is called a “concretion.” If it is banded with concretionary layers of different colored quartz it is called “agate.” If it is partly hollow and lined with crystals it is called a “geode.” Geodes are common in some Mississippian-age strata in Kentucky.

See “How geodes and agates form” pdf

some rounded rock-, or fossil egg-like objects are actually man made.

Some man-made objects are also misidentified as fossil eggs. Circular to oval ceramic balls have periodically been found in creeks and soil in central and eastern Kentucky. Some were used in large vats for mixing paints. Others were used for grinding purposes. One of the clues you can use to determine if an object you find is one of these ceramic balls is to feel the weight of the object in your hand. Does it feel heavy? Possibly, heavier than it should? These ceramic balls were made with barite, which is very dense, so the balls are usually heavy. Also, because they are ceramic, they may feel cold or warm to the touch. Ceramics hold in the temperature of their surroundings well.

Fossil dinosaur eggs

Fossil dinosaur eggs have never been found in Kentucky and are unlikely to ever be found here. Only far western Kentucky, in the Jackson Purchase, has strata of the right age to yield dinosaur fossils. The image above shows what dinosaur eggs look like. The only fossil dinosaur eggs that have been found in North America, are found in the west. They are never found as isolated fossils, but are found in nesting sites, with many eggs arranged in distinct patterns.


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Last Modified on 2021-02-12
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