|CALCITE in Mercenaria permagna
( Calcite Crystals in Fossil clam )
|This plate may be the most significant
specimen of these unique clams ever
|Note the orientation of the Mercenaria clams – most are in “life position”, with the bivalve hinge at the
top. Whatever ecological disaster caused the entrapment of these clams must have been sudden and
overwhelming. Later dissolution of portions of the clam shells and surrounding limestone by fresh
ground water caused supersaturation with respect to calcite, and crystals grew where available large
voids occurred (i.e., inside the clams). The yellow color of the calcite is likely due to traces of iron,
which is present in large amounts in area surficial aquifer system waters. The calcite is fluorescent and
phosphorescent yellow-green under both short and long wave ultraviolet light.
The geological age of this specimen is 1 – 2 million years old (Pliocene – Pleistocene). During this
time, the Kissimmee River valley was a shallow, V-shaped salt water bay, narrow at the northern end
near present-day Orlando and widening to the south in the vicinity of Lake Okeechobee. Rucks’ Pit is
located near the eastern paleo-shoreline of this inland bay. In addition to Mercenaria, other shallow
marine fossils are found within the same stratigraphic horizon. Less commonly, calcified whelks, ark
shells, oysters and other pelecypods turn up, as do calcite-encrusted mangrove roots and seeds. The
matrix is a very highly permeable calcite-cemented mixture of quartz sand, shell fragments and dark
organic matter (the latter presumably mobilized from later, overlying organic-rich sediments or soils).
When collected in situ, most of the rock matrix void spaces are filled with a mixture of quartz sand, shell
fragments and clay, while the Mercenaria clam interiors are largely devoid of sediments, and are
instead filled with fresh ground water.
Rucks’ Pit is now closed, and has been allowed to flood, creating an artificial lake. The property is
being converted into an RV campground. No additional Mercenaria permagna specimens will be
forthcoming from this site.
This specimen is for sale - the asking price is $24,000. We would prefer to see this truly one-of-a-kind
piece reside in a place for all to enjoy, and to that end, we will consider lesser offers from museums
|Rucks’ Pit, near Fort Drum
This is the largest single plate of calcified Mercenaria permagna clams ever
recovered from Rucks’ Pit.
It measures 35 x 25 x 6.9 inches (89 x 63.5 x 17.5 cm), and is home to over 40
The fossil clams are up to 4 inches (10+ cm) in length, and the majority of
them contain amber-yellow calcite crystals.
It was collected during track hoe excavations at the pit in November of 2005.
Specimen preparation was completed during late fall, 2006.
Other than the removal of limestone, clay and sand to better
expose the Mercenaria fossils, no other preparation or
restoration has taken place.
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