Connecticut has a rich mining history that goes back to the early 1700s. The state's igneous and metamorphic rocks provided ideal conditions for mineral formation, whose crystallization created gems coveted worldwide for decorative and industrial purposes Many abandoned mines and quarries exist throughout the state, usually due to everything of value being taken in years past.

Abundant throughout Connecticut and named the state mineral in 1977, garnet is the January birthstone and comes in every color except blue, making it the mineral with the largest variety of colors. Found in many places across the globe, the use of garnet for jewelry and decoration goes back to prehistoric times. From the Latin, "granatus," meaning like a grain, garnet plays a role in the modern age as an abrasive. The U.S. Geological Survey reports that garnet became popular for industrial reasons when Henry Hudson Barton manufactured garnet-coated sandpaper in 1878. In Connecticut, almandine garnet ranks as the most common garnet found, according to the state's official website.

According to U.S. Geological Survey, tourmaline ranks as the first gem mined in the United States by miners of European ancestry, dating back to 1822 in Maine. Like garnet, tourmaline comes in a great variety of colors, and can even have two or three colors in the same gem. For example, the watermelon tourmaline, features a green border surrounding a pink center. Black tourmaline -- the most common color in Connecticut -- can be found not only in mines and quarries, but also out in the open, sticking out of rocks and boulders, reports the state's website.

Danburite -- first discovered in Danbury, Connecticut, in 1839 -- is a rare gemstone that resembles topaz. Its toughness and lack of cleavage allow for cutting into various shapes. Typically colorless or white, danburite also comes shades of yellow, pink and tan, with the AGS Gems website identifying light pink and yellow stones as usually more expensive, due to their rarity. Thought not found as often garnet and tourmaline, other gems uncovered in Connecticut include aquamarine, amethyst, topaz and rose quartz.