This is a nice specimen containing two adjacent Mercenaria permagna clams in and on a dark gray micritic limestone matrix. The left-side clam in the first photo is complete, with a small amount of yellow calcite at the top of the articulated fossil. The right-side clam contains golden yellow trigonal calcite crystals, with the largest measuring about 1.5 cm in length. The shell sides of this clam have been naturally dissolved by slightly acidic ground water (the aqueous source of the calcium carbonate which has recrystallized within the clam), allowing one to see the internal mineralization. The base of the specimen has been sawn flat. The calcite is fluorescent blue-green under shortwave and longwave UV light (see second photo below), and even phosphoresces for a few seconds when the UV light is extinguished. These specimens are Plio–Pleistocene in age (1–2 million years old).