Webster's defines a gem "as any jewel, whether stone, pearl or the like, having value and beauty that are intrinsic and not derived from its setting; a precious or ... semiprecious stone cut and polished for ornament. [or] carved or engraved, as a cameo or intaglio." About 60 kinds of gemstones are found in the United States, only some of which are found in Alabama, as it's not one of the top gem-producing states.
In prehistorc Alabama, native Americans used quartz and other rocks and minerals. In recorded history, quartz is mentioned in the first issue of the "American Journal of Science" in 1819; it was found in the Tennessee River Valley area near Huntsville. Quartz is found all over, however, and chalcedony, which includes many well known varieties of cryptocrystalline quartz, is found in every state, according to the United States Geological Survey. The most important mineral discovery in Alabama occurred in 1831 with the discovery of gold. In 1990 "star blue quartz" became the official gemstone for Alabama.
Agate is a type of quartz and has curved bands of various colors. Look for agate near Garth and Hollytree in Jackson county.
Ermerald and aquamarine are two varieties of beryl, which come in various colors, or are colorless. You can hunt for beryl near Hissop in Coosa county.
There are various types of garnets; they're not all red. You can look for them near Erin, Ashland, and Hollis Corners.
"Rocks & Minerals" lists hematite, marcasite, quartz, olivine, tourmaline, fluorite, agate, jasper, garnet, topaz, malachite, turquoise, diamond, zircon and spinel as gems found in Alabama. It also lists locations, which are broken down into counties, districts and specific sites. Of course, some of these sites are on private property. Another list includes amethyst, beryl (ermerald), calcite, fluorite, gypsum, magnetite, quartz (agate), rutile, tourmaline, turqouise and wavelite. Broken pieces of mussel shells from Alabama are used in pearl production, though not locally. They're inserted in oyster shells for pearl nucleii.
You should be able to find agate, jasper and onyx in the area around Blount. Look for tourmaline near Opelika in Chambers county, Micaville in Cleburne county and Rockford in Coosa county. You can find onyx near Jackson in Clarke county and turquoise in Clay county.