Apatite
The name apatite comes from a Greek word "apatos," meaning deception, which alludes to the mineral's similarity with other more valuable minerals such as olivine, peridot and beryl. It can be transparent to opaque, with color that is typically green but can also be yellow, blue, reddish brown, violet and colorless. This gem exhibits an unusual "partially dissolved" look similar to the look of previously sucked-on hard candy.

Apatite is widely distributed in all rock types, but is usually just found as small grains or fragments. Large and well-formed crystals, though, can be found in certain contact metamorphic rocks; but with a hardness of 5.0 on the Mohs Scale, the softness of apatite prevents wide distribution in the jewelry market. Apatite occurs generally in rather rough prismatic crystals, the largest being 4 inches long and 1 inch in diameter.

In most limestone quarries, careful search shows the presence of small prisms of bright green apatite in the limestone. Notable occurrences include Germany, Brazil, Russia, Myanmar (Burma), Sri Lanka (Ceylon), Canada, East Africa, Sweden, Spain and Mexico.

Earring Back Types

Butterfly Back: A double looped piece resembling a butterfly that fits over a post. Variations on this design are called push back clasps. The basic post and butterfly back are usually used for stud earrings and lighter weight drop earrings.

Hinged Snap Backs: This clasp features a hinged post that snaps into a groove on the back of the earring. It is commonly found on hoops. Sometimes the hinged post is curved to provide more room to fit around the ear, sometimes called a saddleback.

Hook Backs: This earring backing is simply a long, bent post that fits through the piercing. Hooks have several variations, most notably the shepherd's hook and the French hook. While thin wire hooks reduce the weight of long earrings, making them more comfortable, they aren't as secure as other clasp styles.

Lever Back: A hinged lever snaps shut against the curved post to form a closed loop around the ear lobe. This clasp is very secure and good for large or medium sized styles that drop just below the ear.

Omega: Also called French clips, this clasp has a straight post and a looped lever. The hinged lever closes around the post and is held against the ear with pressure. The omega clasp is the most secure clasp, especially for the larger, heavier earrings.

Screw back: This backing is a slight variation of the standard post and butterfly nut back. Instead of pushing on the back, the nut twists onto the threaded post. A screw back post design is often preferred for expensive diamond stud earrings that require increased security.