Once considered more valuable than diamonds, a peridot ring is a must have. This "gem of the sun" is the birthstone of August and is a beautiful match for the lush green tapestry of late summer. Once considered more valuable than diamonds, a peridot ring is a must have. This "gem of the sun" is the birthstone of August and is a beautiful match for the lush green tapestry of late summer. Sapphire is the birthstone of September, and one of the most popular gemstones on the jewelry scene today. The deep blue color of a sapphire ring is just right for an evening out.