Where is Fossil Coral found?
Silicified Coral
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Open the appFossil Coral occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Fossil Coral
Florida, USA
Known for Oligocene-Miocene age silicified corals, particularly from the Tampa Bay area and along the Gulf Coast. These often exhibit intricate patterns and a range of colors.
Michigan, USA
Famous for the Devonian-age 'Petoskey Stone' (Hexagonaria percarinata), a specific type of fossil coral with distinctive hexagonal patterns, found primarily around Lake Michigan.
Indonesia (especially Sumatra)
Produces large quantities of beautifully patterned and colored fossil corals, often from Miocene-Pliocene deposits. These are widely used in lapidary and decorative arts.
Utah, USA
Various localities yield silicified corals, often associated with marine sedimentary units.
Georgia, USA
Some occurrences of silicified coral have been reported.
Morocco
Known for various fossiliferous deposits, including some silicified corals.
Collecting tips
- Look in Marine Sedimentary Deposits. Focus on areas known for ancient marine limestones, shales, or sandstones that were once coral reef environments. Riverbeds and beach gravels in such regions can also yield tumbled specimens.
- Identify Coral Patterns. The key to identifying fossil coral is the presence of preserved coral structures. Look for radial septa, hexagonal patterns, or other colonial coral morphologies. Polishing a small area can reveal these patterns more clearly.
- Check Hardness. Fossil coral, being silicified, will be hard (Mohs 6.5-7). It will scratch glass and will not be scratched by a steel knife. This distinguishes it from un-silicified calcium carbonate corals (Mohs 3-4).
- Acid Test (Caution Recommended). A small drop of dilute hydrochloric acid will not react with silicified coral, whereas un-silicified calcium carbonate coral will effervesce. Use this test sparingly and with caution, as it can damage the specimen.
- Examine Luster. Freshly broken or polished surfaces should exhibit a waxy to vitreous luster characteristic of chalcedony.
Quick Check
- Color:
- Variable (white, gray, brown, black, pink, red, yellow, orange)
- Luster:
- Waxy to vitreous (polished), dull to earthy (unpolished)
- Streak:
- White
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