Greek and Roman jewelry was very important to the people who wore it. It sometimes had symbolic meaning, was decorative, or even showed status just like their clothes did. Early Greek and Roman jewelry was made of many different materials that came from many different place because of the accessibility to a variety of natural resources found in Europe all the way to Asia. They also had a very big trade industry and that helped them access precious gems and fine metals to create the jewelry.
A lot of the jewelry they would where would have a functional purpose. They were the first people to wear brooches, but they used them as a way to hold together their clothes instead of a decorative accessory like we use them today. They also wore something called the fibula, which basically was a glorified safety pin that also was used to hold together their clothes, and was usually decorated with beautiful gemstones.
Greek and Roman jewelry generally was not as shall I say "bling bling" as some of the jewelry you will see from other Mediterranean cultures. They were as interested in what it looked like, but rather more interested in what it did. Although due to trade and travel eventually you will eventually see more detailed jewelry as the Greeks and Romans progressed. In a way it is like any fad, if someone important thinks it is beautiful then everyone will start thinking it is beautiful and wanting one of their own.
Here are some examples of the jewelry I was talking about.
Rings: vroma.org (left), Roman Earring: IAA
Roman Earrings: www.vroma.org
The variety of gemstones that were used in their jewelry was also very important. They had beautiful pearls that came from the coast, and onyx and emerald especially. Another example that we still wear today is the hoop earring which started in Rome. Their earrings looked a little different but generally had the same function which was to complete and outfit. A lot of the pictures I looked at of their hoop earrings depicted images or miniature sculptures of animals, gods, and slaves all showing meaning in their lives.
Now here are some similar pieces that are made today for a much cheaper price than what the Greeks and Romans paid.