Identification: Agate, or chalcedony, is a variety of cryptocrystalline quartz (SiO2). It is found in a variety of colors, typically gray, brown, black, white, and sometimes red. Fossil corals and mollusks may be replaced with agate deposited by silica-rich ground water percolating through limestone. In 1979 the Florida Legislature designated agatized coral as the Florida State Stone. It is described in the statute as “a chalcedony pseudomorph after coral, appearing as limestone geodes lined with botryoidal agate or quartz crystals and drusy quartz fingers, indigenous to Florida.”

Occurrence: Much of Florida’s agate, including the Tampa Bay agatized coral, formed in the Oligocene-Miocene Hawthorn Group sediments. Once abundant at Ballast Point in Tampa, it is occasionally dredged up in the Tampa and Clearwater areas. It also occurs in limestones along the Econfina, Withlachoochee and Suwannee Rivers. An Oligocene variety is sometimes found in Suwannee Limestone quarries north of Tampa.

Use: Agatized coral, particularly in the form of large geodes, is prized by gem and mineral collectors.

 The Anastasia Formation is composed of Pleistocene interbedded sands and coquinoid limestones. The most recognized form of the Anastasia is an orangish brown coquina consisting of whole and fragmented mollusk shells in a matrix of sand, cemented by calcite. Coquina has been used as a building stone in Florida for over 400 years. It is found at land surface along the east coast from St. Johns to Palm Beach Counties, and may occur up to twenty miles inland from the coast in the subsurface. Excellent exposures occur at Washington Oaks State Park, in Flagler County, at the House of Refuge on Hutchinson Island in Martin County, at Blowing Rocks Preserve in Palm Beach County, and along Country Club Road in Palm Beach County.

 The Avon Park Formation is composed of cream to light-brown or tan, Middle Eocene, fossiliferous marine limestone interbedded with dolostone. In a few areas of west-central Florida, molds of evaporites may be present in the dolostone. The Avon Park Formation occurs throughout the Florida peninsula and the eastern panhandle. It comprises the oldest rock cropping out in Florida. These sediments are locally exposed in sinks and quarries near the crest of the Ocala Platform in Citrus and Levy Counties. Avon Park fossils include mollusks, foraminifera, echinoids, algae, and carbonized plant remains.

 The Caloosahatchee Formation consists of Plio-Pleistocene fossiliferous quartz sand with variable amounts of carbonate matrix interbedded with variable sandy, shelly limestones. Mollusks are typically the predominant fossils, along with corals, bryozoans, echinoids, and vertebrates. Fresh water limestones are commonly present within this unit. Classic exposures of the formation occur along the Caloosahatchee River in Lee and Charlotte Counties.

 The Chattahoochee Formation is an (Lower Miocene) see time scale, predominantly fine-grained, often fossiliferous, silty to sandy dolostone and limestone. Fossils include mollusks and foraminifera. The Chattahoochee Formation occurs in a limited area of the central panhandle from Walton County westward into Leon County. A classic exposure occurs along the entrance road to the Jim Woodruff Dam in Chattahoochee, Gadsden County.

 Identification: Chert, also known in Florida as flint or flint rock, is an extremely fine-grained variety of the mineral quartz. It is characterized by its extreme hardness (7.0), glass-like fracture, and the sharpness of the edges of broken fragments, Florida's cherts are generally gray in color, though some are bright shades of blue, red, yellow and orange.

Occurrence: Chert is found in Florida in association with some of the limestone formations, especially the Ocala. The material was formed by the replacement of calcium carbonate with silica carried in circulation ground water, as shown by the fact that much of the chert still contains traces of the fossils that were present in the original limestone. Chert is found at the surface of the ground in many of the northern and western counties of the State, especially Wakulla, Marion, and Citrus counties.

Production and Use: Chert was utilized by Florida's Indians in the manufacturing of axe heads, spear heads and arrow points. The hardness and variety of colors make chert suitable as a semi-precious stone.

 The Key Largo limestone is a Pleistocene, white to light gray marine limestone, which contains numerous fossil corals. Some of these corals have been partially dissolved by ground water and the spaces remaining filled with crystalline calcite. The Key Largo limestone is found at the land surface in the Florida Keys from Sand Key to Loggerhead Key. An excellent exposure may be fiewed at Windley Key Fossil Reef Geological State Park, at mile marker 85.5 in the keys.

 The Marianna Limestone is a Lower Oligocene, white to cream, fossiliferous, variably argillaceous marine limestone occurring in the central panhandle. It is laterally equivalent to the lower portion of the Suwannee Limestone. The Marianna Limestone was once quarried near Marianna, Jackson County, for use as a building stone. Fossils include foraminifera, mollusks, and rare vertebrates.

 The Miami Limestone (formerly the Miami Oolite) is a Pleistocene marine limestone. It occurs at or near the surface in southeastern peninsular Florida from Palm Beach County to Dade and Monroe Counties and in the keys from Big Pine Key to the Marquesas Keys. The Miami Limestone consists of two facies: an oolitic facies and a bryozoan facies. The oolitic facies consists of white to orangish gray, oolitic limestone with scattered concentrations of fossils. Ooliths are small rounded grains so named because they look like fish eggs. Ooliths are formed by the deposition of layers of calcite around tiny particles, such as sand grains or shell fragments. The bryozoan facies consists of white to orangish gray, sandy, fossiliferous limestone. Beds of quartz sand and limey sandstones may also be present. Fossils present include mollusks, bryozoans, and corals. An excellent exposure is observable at Alice Wainright Park, in Coral Gables, Dade County.

 The Ocala Limestone consists of white to cream, Upper Eocene marine limestones and occasional dolostones. Generally the Ocala Limestone is soft and porous, but in places it is hard and dense because of cementation of the particles by crystalline calcite. The deposit is remarkable in that it is composed of almost pure calcium carbonate: shells of sea creatures and very tiny chalky particles. Ocala Limestone underlies almost all of Florida, but it is found at the surface of the land only in a small portion of the state. It is mined for use as roadbase and cement where it is close to the surface in west-central Florida and the northwestern peninsula. Fossils present in the Ocala Limestone include abundant large and smaller foraminifers, echinoids, bryozoans, mollusks and rare vertebrates.

 The St. Marks Formation is a white to yellowish gray, sandy, fossiliferous Lower Miocene marine limestone. It is exposed in sinks and streambeds in Wakulla, Leon and western Jefferson Counties. Mollusk molds and casts are often abundant.

 The Suwannee Limestone, is a white to cream, fossiliferous, Lower Oligocene marine limestone. Dolomitized portions of the unit are gray, tan, light brown to moderate brown, dolostone with limited occurrences of fosiliferous (molds and casts) beds. Silicified limestone, in the form of chert, is common in Suwannee Limestone. It occurs near the surface in the eastern panhandle, northern peninsula, and in portions of west central Florida. Fossils present in the Suwannee Limestone include mollusks, foraminifers, corals and echinoids. Classic exposures occur along the Suwannee River in Suwannee and Hamilton Counties.

 The Tamiami Formation is a Pliocene marine unit comprising a wide range of rock types, including: light gray to tan fossiliferous sands, light gray to green fossiliferous sandy clays and clayey sands, and white to light gray, poorly consolidated, sandy, fossiliferous limestone. Phosphate is present in virtually all lithologies as limited quantities of sand- to gravel-sized grains. Fossils present in the Tamiami occur as molds, casts and original material. The fossils present include barnacles, mollusks, corals, echinoids, foraminifers and calcareous nannoplankton. It occurs at or near the land surface in Charlotte, Lee, Hendry, Collier and Monroe Counties in the southern peninsula.

 The Tampa Member (formerly Tampa Limestone) of the Arcadia Formation is a white to light gray, fossiliferous, Upper Oligocene to Lower Miocene marine limestone containing variable amounts of dolostone, sand, clay, and phosphate. The Tampa is usually a hard, massive crystalline rock and in some areas it contains small cavities called molds where shells have been dissolved out of the rock. Fossils include mollusks, foraminifera, and algae. The classic outcrop areas are at Ballast Point and Six-Mile Creek areas in Tampa, Hillsborough County. This unit is well-known for its silicified fossils, including agatized coral, Florida’s State Stone.