Maryland might not have the rich rare gem deposits of western states such as California and Utah, but the Mid Atlantic state is an abundant home to a few types of gems. Maryland even has its own official state gem. More rarely, people have discovered other precious stones in Maryland.
The hard, silicate mineral beryl occurs as part of the natural geography in central Maryland. The area is a part of the Appalachian/Piedmont region, which stretches from central Maryland through Pennsylvania, northern New Jersey, southeastern New York all the way to the tip of western New Hampshire, and beryl is common in the region. Beryl in the region most frequently develops within granite and pegmatites, a coarse, volcanic rock. Vivid green emeralds and blue aquamarines both are forms of beryl, but these types of beryl are not found in Maryland. Beryl also is a source of the rare element beryllium.
You probably associate pearls with oysters, but any bivalve can produce a pearl, including the hard-shell clams found in coastal Maryland. Like oysters, clams produce pearls when a piece of grit gets inside their shells. They coat the grit with shell material, making it smoother and more comfortable for the clam, ultimately producing a pearl. Clam pearls generally are a mixture of purple and white in color. The pearls are not particularly rare and are not frequently harvested, according to The Press of Atlantic City. Clam pearls vary in shape and size, and some can be valued at thousands of dollars.
In 2004, Governor Bob Ehrlich signed legislation naming the Patuxent River Stone as Maryland's official state gem. The stone, named for the Chesapeake Bay tributary in which it appears, is a form of quartz found only in Maryland, according to the Maryland State Archives. Appropriately, iron gives the stone a red and yellow hue, the same colors as Maryland's state flag. The stone has been a subject of controversy among gem and mineral enthusiasts, however, thanks to the state's description of it as an agate, a specific form of quartz. Baltimore Mineral Society program director Jake Slagle says agates generally are not found in Maryland.
The Mindat Directory, a database on mineral discoveries, lists several other gems that, while not widely common, have been discovered in Maryland over the past several decades. These include goethite and garnets in Baltimore County, calcite and malachite in Carroll County, serpentine in Cecil County and pyrite and opal in Montgomery County.