Do you have any pictures of the crystal rocks?
They could be from a lost collection, or if green and near 1715 wreck locations - emeralds.
Or maybe agatized coral from Pinellas County:
Florida's only crystal rock of note is agatized coral, which is not the same as other coral specimens. Agatized coral is a highly prized gemstone internationally and became Florida's state stone in 1979. It forms when silica, which is abundant in the Gulf of Mexico, hardens into quartz within coral, and it retains the coral's shape. Trace minerals cause the agatized coral to take on a variety of colors. In its many shapes and sizes, agatized coral resembles coral. The best time to look for agatized coral is when the water level is low
Read more: Where to Find Crystal Rocks in Pinellas County, Florida | eHow