"The sand and shell matrix rock is in the Nashua Formation (Pleistocene) and is composed of well-calcified shells. Any cavities within these fossils may contain calcite crystals. Honey colored calcite crystals up to 1" in length can be found within large fossilized clamshells. Small calcite crystals within shells are very common." - Rucks' Pit website
"SPC students and the Science Adventurers Club on a fossil dig. The object of our intense concentration you see here, are fossilized marine clams that were buried and then fossilized during a sea level drop. The calcium partially dissolves during ground water seepage and re-crystalizes with other minerals as calcite crystals that form in any empty spaces. Thus the clams are full of shiny, beautiful amber colored crystals. There is only one place where the public can dig, and these fossils are unique to Florida. Dig we did! At the end of a dirty day we were tired, but everyone found at least a few keepers, and some brought home one or two 5-gallon buckets-full! Here we all are tunneling our way through the 1-4 million year old deposits to find our treasures." - Dr. Monica Lara
See more images here: Clam Dig Spring 2012