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Crystals Instead of Pearls
On a cloudless morning in Southern Florida, the first rays of the sun cast a glow on a large shell mine near Ft. Drum. It is barely 50 feet deep below the surrounding flat desolate tracts of palmetto bushes but is distinguished by one prominent feature: a trench cutting through its rubble strewn floor. If your imagination is keen enough, the isolated trench might resemble a rock-lined canal in some far away exotic land – perhaps to bring water to some Inca temple. However it is a slice through Florida's geological history.
With hammers swinging, pick axes picking and shovels shoveling a crowd of amateur rock collectors were scouring every inch of the trench. What is the prize? Fossil shells lined with calcite crystals. Not just any calcite crystals, mind you, but the coveted form called dog's tooth spar - but an even rarer form that is tinted amber brown. Like pearl divers opening oysters in hopes of finding a pearl, the collectors carefully opened each clam with the desire of discovering crystals.
Known as the Fort Drum Crystal Mine[1] - this site it has something for everyone. Some hunt them for specimens in their fossil collection while others see them as minerals. “These are minerals, not fossils,” one collector exclaimed, “I do not collect rocks that were once dead animals.”
While the trench may hold untouched specimens for the hardy, some collectors search through the spoil piles excavated from the trench. These trench-tailings offer museum quality specimens to the patient and sharp eyed hunter. Either way, bragging-quality specimens are there waiting discovery.
Mine owner, Mr. Ruck, with his hat-band lined with crystals reminding one of a rock-hound version of Crocodile Dundy, will appear nearby to keep a watch on the crystal hunters. Luckily he did not see me walking the creek bottom in a side canal. It was firm and then suddenly I found myself waist deep in mud, or perhaps it was quicksand. Feeling like a trapped animal must have felt in the La Brea Tar Pits, I quickly latched onto the rock face of the trench. A helping hand shot out to pull me free. Two minutes later another hapless adventurer stepped into the same trap. Everyone’s advice, wear old clothes and expect to get wet.
Although the mine is famous for its crystal lined fossil shells, it is also well known for its rare fossil shells. For example, in the lowest formation, the Tamiami formation, several species of cowries, cones and other collectable fossil shells are eagerly sought by fossil shell collectors. "This is a real scientific resource” muses Ed Petuch, author of several prestigious guide books on Florida’s fossil shells[2] and having named hundreds of species of fossil mollusks, “but also a mecca for the serious collector.” In fact several species discovered in this pit bear the name of the owner, for example, Siphocypraea rucksorum, Urosalpinx rucksorum, Busycon rucksorum, Oliva rucksorum and Ventrilia rucksorum. Additionally, several yet unnamed species are awaiting their scientific names that were discovered here. According to Petuch, the mine was an area flooded several times with sea water in the past 3 million years. There exist six thick beds as evidence of these inundations. In between each bed are layers of non-marine origin indicating dry land conditions – seven of which have been identified. The two most important formations in which collectors target are the Nashua Formation and Tamiami Formation. The Nashua Formation, spanning 1.8 to 2.3 million years ago, contains the highly desirable calcite crystals whereas the Tamiami Formation awards us with rare fossil shells dating from 2.6 to 3 million years.
Do the industrious collectors really care about formations, eras or other scientific details? Actually, I was impressed that almost everyone there could identify the age and point out the various exposed formations. Even more amazing was the expertness demonstrated by the collectors in identifying the various shells – as if Latin were their second language.
What is the future of this wonderful resource? The mine is bound by both natural and legal limitations. On some edges there no longer exist shells. A string of power lines impose a limit on another edge. A tiny wooded area may be the last mining activity and after that only memories and specimens in collections and museums will testify to the excitement once experienced in this manmade crater.
- submitted by Bill Hoefer
The thrill of discovering crystals cannot be described adequately but those who experience it will tell you it is exciting. For some collectors, the thrill of identifying their treasures is almost as fun. The crystals are easy to identify but the shells are another challenge.
Identification of every species found in the Fort Drum Crystal Mine is not the goal of this article. In fact a book[3] is available that details the geological history and has an important identification portion - these identifications are based upon that book.
Most prized are the clams with calcite crystals - Mercanaria permagna (Conrad 1838). Here is one with crystals, dog tooth and drusy, and one that may or may not have a prize.
Even more sought after are the Busycon ruckorum (Petuch 1994) geodes. Here is one with crystals and one without a treasure.
Olives are commonplace and usually are one of these three species:
Oliva roasae (Petuch 1991)
Oliva carolinensis (Conrad 1863)
Oliva rucksorum (Petuch 1994)
A diminutive olive is also found there, namely Olivella carolinae (Gardner 1948).
Often overlooked are the small, but nevertheless quite collectible, marginella shells such as Prunum bellum (Conrad 1868).
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