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Florida State Symbols: State Stone Agatized Coral

06.19.2016

Florida has a state stone and a state gem, although technically speaking, their state stone is a fossil.  I'll begin with the state stone, agatized coral (a.k.a. silicated coral and fossil coral). 

Coral is the external skeleton of ocean polyps; it's mostly lime.  When the polyps die, over time silica from water replaces the lime, creating what is called a pseudomorph (one mineral has been replaced by another mineral without losing the original form and shape). This process takes 20+ million years to occur.  Most of the Florida agatized corals are from the Oligocene-Miocene period.

Trace minerals give these fossil corals a variety of colors:  white, gray, brown, black, yellow, peach, orange, tan, amber and red.

This first picture is of a coral nodule that has been sliced in two and is from Fossil-Treasures-of-Florida.com.

While most living corals are now protected, fossil corals are not.  Most of the agatized corals were originally rugose and tabular coral species.  The oldest fossil corals are over 450 years old!  This photo is of a pile of fossil corals from the Withlacooche River and was taken by River Rat and posted on the Fossil Forum.

Because it's now quartz (silica), agatized coral is a 7 on the Mohs scale so it is quite hard and has long wear as a cut stone.  The first humans to inhabit Florida used the agatized coral to make tools such as spear points and knives.  Archeologists have found tools dated as old as 5000 years old near St. Petersburg.

This pile of fossil corals cut into cabochons is from ereferencedesk.com and shows the range of colors available.

Agatized corals are found in three primary locations in Florida:  Tampa Bay  near Ballas Point; the Econfine River; and the Withlacoochee/Suwannee River beds. This last picture is a close up of an agatized coral cab from Florida that I found on Pinterest with no indication of who actually took the picture (my apologies to the photographer).

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