Turtlestones
The turtlestones of Conesus NY are actually a geologic feature known as a Concretion. Concretions form in sedimentary rocks when minerals dissolved in ground water precipitate around a nucleus. Common minerals in this area include calcite (CaCO3) and siderite (FeCO3). Because the concretions are harder than the surrounding rocks, they are often left behind after the softer host rock has weathered away. They are mostly spherical or oblong but can also have an irregular shape. Some concretions develop cracks known as septaria that become filled with coarser grained minerals such as calcite. These cracks make the outside of the concretion resemble the back of a turtle. Sometimes the center of the concretion is hollow, making room for larger crystals to grow. This type of concretion is referred to as a geode.
The rocks in this area were deposited in shallow seas during the Upper Devonian and are between 383 to 359 million years in age. Many of the concretions in this area come from the West Hill and Gardeau Formations that consists of a mixture of gray siltstones and shales.
Logging requirements:
How would you describe these turtlestones?
To get credit for this cache e-mail me your answers to the following questions:
What is the length of the largest turtlestone on display? (It’s OK to estimate)
What is the technical name for a turtlestone?
Do you think any of the turtlestones on display are geodes? If so, what observation lead you to this conclusion?