The name of semi precious gemstones is largely derived from the characteristics that the gemstone displays. For instance ruby gets its name from the Latin word rubrum which means red. Another gemstone that takes its name from its color is Emerald. It comes from a Persian word that means green.
Garnet, on the other hand, derives its name from granatum, which is the Latin word for pomegranate, because of its resemblance to pomegranate seeds. Amethyst owes its name to a completely different thought. It comes from the Greek amethustos, which means "not to intoxicate." Amethyst was often worn by ancient Greeks to fight intoxication.
Aquamarine is the Latin for seawater because it is a greenish-blue in color. Incidentally, this stone has been used as a protection by sailors throughout history. The sparkling Diamond derives its name from the Greek word adamas, which means unconquerable. This was a very appropriate name to give to diamond because it is the hardest substance known to man.
Peridot, which is the birthstone of Leos, derives its name from the Arabic faridat, or "gem." These stones were specially prized by Egyptians, and were mined in the night when they were easily visible.
Sapphire also has a part of its meaning coming from the color blue, which is the most common color of Sapphires. The Persians believed that the blue of the sky was the reflection of a great sapphire on which the Earth rested.
Opal comes from the Sanskrit word upala, which means the precious stone. Topaz too takes its name from the Sanskrit word tapas, which means fire.
The moonstone derives its name from its pristine, white color which makes it resemble the moon. Similarly, Watermelon Tourmaline, is named after the fruit watermelon because it is green outside and pink inside.