A few years ago, I was working a project in northern Jefferson Co. Ky. that was in the preliminary stages of development. As such, the area had been stripped of vegetation leaving a vast field of regolith that was a mud pit when it rained… sticky clayey mud. But, those rains also uncovered thousands of silicified fossils that littered the ground of the project.
One of the larger pieces that I picked up was a head of the tabulate coral Alveolites. It was fossilized as silica replacement that is common of many fossils in the Jeffersonville Limestone.
A view of the base of the colony
The top of the colony
The individual corallites are about 2mm diameter.
Advertisement
Tags: alveolites, cnindaria, devonian, Fossil, kentucky
February 5, 2011 at 1:22 pm |
ok to print entire
The most well known type of Agatized Coral is found at Tampa,
Florida, and is, in fact, part of a geological feature called the
Tampa Formation. From about the time of the Oligocene-Miocene
boundary, these fossils are pseudomorphic replacements in agate
(Chalcedony) of corals which existed around 20 million years ago.
Some are extinct species, and fairly rare. Several of the species
from the area actually bear the name of this locale, such as Goniopora
ballistensis, or Acropora tampaensis. There is even Porites
floridaeprima.
Almost all the Tampa coral specimens are very nice geodes and
highly collectible. They can be located on the beaches at Ballast
Point Pier (Jules Verne Park, off Bayshore Boulevard) at low tide, and
also a little further south at Shell Point Road, where it meets the
bay. In between these two points is the main source of Tampa Bay
Agatized Coral. At Ballast Point and environs, the reds, blacks, and
blues are the most sought after, and in my experience only about 40%
of the geodes from Tampa are visibly crystalline, but the ones that do
have visible crystals are nothing short of magnificent.
Winter tides are sometimes extreme in Tampa Bay, and thats when
most of the diggers and collectors are out on the flats, collecting
this rare and beautiful fossil material. There are other places
around Tampa Bay to find Agatized Coral, and its always good to check
spill islands and dredged areas around Tampa for fossils of all kinds.
You never know what you will find.
Another type of Agatized Coral, though less well known, can be
found around Perry, Florida, along the paper-mill road-cuts out by the
Gulf of Mexico, south of Goose Pasture. A lot of looking is
necessary, and the locals are not helpful at all. The Perry Agatized
Coral is manifest as geodes too, and seems older than the Tampa
Agatized Coral. The outer crusts and most other fossil evidence of
coral have been eradicated by time from the Perry pseudomorphs, and
most of the interiors of these geodes are extremely fine druse
crystal. There have been leases taken on some of the pockets of this
coral over time, and though it is said to be depleted, that is never
the case. It is just harder to get. There are some nice agatized
shells and echinoids to be found in that same area as well.
Another fairly well known source of Agatized Coral in the same
general area is at the Withlacoochee river, near Valdosta, Georgia.
Leave interstate 75 at the Valdosta exit, and go west 5 miles on
Highway 31 to Clyattville. Take main street west 1.5 miles, then
south on Blands Dairy Road 4 miles to the river. Collecting can only
be done during low water conditions. This coral is comprised of large
heads, or pieces of heads, and about 75% of it is good quartz crystal
inside, very nice.
Almost every state and country has some form of fossil coral, and
much of it has been silicified in an attractive manner. Many times
the polyps of these formations posess patterns and designs from the
way they grew; when cut with a diamond saw, then polished into cabs or
beads, the material may be attractive enough to be called gemstones.
I recently discovered a fine type of Agatized Coral in New York, from
a deep fossil layer within a limestone quarry. It is blue agate and
will cut some fine stones. It was in very limited quantity, but that
makes it that much more desirable. There is bound to be some fossil
coral near your locale too, and though it may not be of lapidary
grade, perhaps it will lead you to better things one day, or be
valuable for its geological information. Good Luck.
Agatized Coral Gemstones
By Bill Gallagher
2010
April 14, 2011 at 8:25 pm |
I have a heliolitide-tabulated coral about 4″ in diameter…afte a geologist confirmed its identity..he told me that it is very rare and he has never seen one in such good shape…it is estimated to be close to 550 million years old…who could I contact to unload this piece?
April 18, 2011 at 3:45 pm |
He probably got the age wrong as tabulates didn’t evolve until the Ordovician. Too, rarity and fossils are relative terms as all fossils are rare, but can be commonly found.
If you are looking to sell it, post it to Ebay.