Gems

Gems, also known as jewels, areprecious stones that are found buried all around in Equestria, as shown in A Dog and Pony Show. Fashionistas like Rarity are known to use these gems to decorate and embroid their designs and tailoring outfits. Ponies, especially most mares, apparently have a great affinity towards gems, as they greatly admire their beauty. This is possibly a normal thing as gems are often regarded as jewelery.

Dragons find gems edible, and they consider them a great delicacy. Dragons like Spike are notably known to find gems as irresistibly delicious; wild dragons are known to build their nests from gems and other precious items. However, there are other creatures in Equestria whom often go after gems. Diamond Dogs, for example, tend to live close to or within areas where there are extensive depositories for gems. These dogs instinctively dig and collect gems their whole lives. It is currently unknown why Diamond Dogs always collect gems though.

Ponies regard gems as mere trinkets, and unlike gold Bits, gems apparently have no monetary value. This may be because gems are not as rare as they are usually perceived in real life. Although not relatively common, gems seem to be available in great bunches where they are available under the ground. Any creature can merely dig them out should they find any. However, it is the task of finding the gems' deposits which is usually difficult. This is apparent, as in the episode A Dog and Pony Show, Diamond Dogs ponynapped Rarity specifically for her special, magical abilities in finding gems instantaneously.

As shown in A Dog and Pony Show and The Cutie Mark Chronicles, finding gems, and by extent the spell used to find them, is Rarity's special talent.

Trivia

 * It is not normal to actually find various gems by the bunches in the same spots, nor is it normal to find them already fine-cut. Contrary to popular belief, gems when mined or dug out tend to look like common rocks, having deformed shapes and mixed with other composites. It is not until they are processed that they take form as found on market jewelery.