A diamond, the hardest known natural material, and is a carbon crystal. Diamonds are famed for their hardness (58x harder than any other substance on the earth), and for their high refractive index. Diamonds form under high temperature and pressure conditions that exist only about 100 miles beneath the earth’s surface. Diamonds are the birthstone for April. Diamonds are also the gem that marks the 60th and 75th wedding anniversaries. Diamonds are the only gem composed of one single element: carbon. Most diamonds formed more than a billion years ago, deep in the earth’s mantle.
Alexandrite appears green in natural sunlight and red in man-made light. Often called “emerald by day, ruby by night,” alexandrite a rare color-changing variety of the mineral chrysoberyl. Discovered in Russia’s Ural Mountains in the 1830s, it’s now found in Sri Lanka, East Africa, and Brazil, but it is exceptionally rare and valuable. Alexandrite is the birthstone for June along with pearl and moonstone. Alexandrite is also the gem for the 55th wedding anniversary.
Peridot is one of the few gemstones that occur in only one color, an olive-green. The intensity and tint of the green, however, depends on how much iron is contained in the crystal structure, so the color of individual peridot gems can vary from yellow to olive to brownish-green. The most valued color is a dark olive-green.
Tourmaline comes in a wide variety of colors and has one of the widest color ranges of any gem. Tourmaline is a birthstone for October, along with opal. Tourmaline is also the gem of the eighth anniversary.
Corundum is the second hardest natural stone after diamonds. The most popular color of corundum is blue or commonly known as a sapphire. When corundum is red, we call it a ruby. Corundum exists in all colors – white, yellow, etc.
The most famous kind of beryl is green beryl or an emerald. When it is pink, we call it morganite. Morganite can be quite large in size and was named after financier J.P. Morgan. Aquamarine is blue beryl. Yellow beryl is heliadore, purple beryl is kunzite.