January – Garnet
Garnets are a group of minerals that are very much alike. These gemstones come in almost every color. Red is the most common garnet color, and is found in metamorphic rocks around the world. Other colors like green, orange, and purple-red are less common and more valuable.
February – Amethyst
Amethyst was as expensive as ruby and emerald until the 19th Century, when Brazil’s large deposits were discovered. It was believed to prevent intoxication—amethystos means “not drunk” in ancient Greek. Today, as the most valued quartz variety, amethyst is in demand for designer pieces and mass-market jewelry alike, and its purple to pastel hues retain wide consumer appeal.
March – Aquamarine
Aquamarine’s name comes from the Latin for seawater and it was said to calm waves and keep sailors safe at sea. March’s birthstone was also thought to enhance the happiness of marriages. The best gems combine high clarity with limpid transparency and blue to slightly greenish blue hues. Like many beryls, aquamarine forms large crystals suitable for sizable fashioned gems and carvings.
April – Diamond
Most diamonds formed more than a billion years ago! They form about 100 miles (161 kilometers) below the earth’s surface, where the temperature and pressure are just right. Diamonds are the hardest natural material on earth. They stand for fearlessness and invincibility, and are a symbol of love.
May – Emerald
Emerald is the green variety of the mineral beryl. (Beryl also includes aquamarine.) There are small amounts of certain atoms that make the emerald bluish-green to green. The age of the oldest emeralds from South Africa is almost 3 billion years old!
June – Pearl, Alexandrite, Moonstone
Pearl is an organic gem, because it comes from a living marine creature. Pearls form in oysters and other mollusks. The mollusks form the pearl around an object that enters their bodies. Cultured pearls grow in mollusks raised by humans who help them to form pearls. Natural pearls form without any human help. Both are beautiful and valuable, and come in white and other colors.
Often described by gem aficionados as “emerald by day, ruby by night,” alexandrite is the very rare color-change variety of the mineral chrysoberyl. Originally discovered in Russia’s Ural Mountains in the 1830s, it’s now found in Sri Lanka, East Africa, and Brazil, but fine material is exceptionally rare and valuable.
Moonstone is a mixture of two feldspar minerals that are layered inside the stone. When light falls between these layers, it scatters in many directions. This causes the phenomenon called adolescence. This is a light that seems to move across a gemstone. It really glows! The finest moonstone is colorless with a blue sheen.
July – Ruby
Ruby is famous for the beauty of its red color. Red represents strong emotions like love and anger. The most famous rubies are found in marble, a metamorphic rock. These have rich red color and usually glow a bright red under sunlight. The glow makes the red color even stronger. Darker rubies are found in igneous rock.
August – Peridot, Spinel
Famous for its color, peridot can be brownish-green to yellowish-green to greenish-yellow to pure green. Pure green stones are rare. Most peridots are formed deep inside the earth and are brought to the surface by volcanoes. And did you know some peridots came to earths in meteorites? Peridot from outer space is really rare, however.
For centuries, people thought spinel was ruby. It was discovered to be a separate mineral a couple of centuries ago. Even so, spinel is loved for its rich red color and history. Its crystal structure and the different colors it comes in make it special, too. Collectors love spinal crystals that are shaped nicely. Red spinel is the most popular, but it is also blue, hot pink, and bright orange.
September – Sapphire
Sapphire is corumdum, the same type of mineral as ruby, except that it is not red. Sapphire is famous for its blue color, but it also comes in many other colors, such as orange and pink. They are called fancy sapphires. There are also color changes sapphires which change color under different lighting. Some sapphires even show a phenomenon called asterism. A star appears on the face of the stone.
October – Opal, Tourmaline
Opal flashes colors as you turn the stone or move around it. This phenomenon is called play-of-color. An opal might show a single color, two or three colors, or all the colors of the rainbow! The best play-of-color is the brightest; if it also has all the rainbow colors, then it is very rare and valuable. Opals are known by their background colors and are called black, white, gray, or fire opals.
Tourmaline is famous for its dazzling colors. There are rich reds, pastel pinks, peach colors, strong greens, bright yellows, and deep blues. Some have more than one color, like watermelon, which is pink in the middle and green around the outside. People confused tourmaline with other gems, like emeralds and rubies, until the 1800s. That’s when scientists recognized tourmaline as a unique mineral.
November – Topaz, Citrine
Many people think of topaz as a blue gemstone, but it also comes in shades of yellow, orange, red, pink, purple, and brown. Imperial topaz is a reddish orange to orange- red, and is very expensive. Sherry topaz is yellowish brown to orange. It is often called “precious” to tell it apart from other, less expensive stones that are a similar color.
Citrine is rare in nature. In the days before modern gemology, its tawny color caused it to be confused with topaz. Today, its attractive color, plus the durability and affordability it shares with most other quartzes, makes it the top-selling yellow-to-orange gem. In the contemporary market, citrine’s most popular shade is an earthy, deep, brownish or reddish orange.
December – Turquoise, Tanzanite
Turquoise is a colored stone found only in places that are dry and barren. People like its color and its rich history. The colors of this stone range from different shades of green to a bright sky blue called “robin’s-egg” blue. In the U.S., it is famous for its jewelry made by Native Americans. It also has a rich history with the ancient Egyptians and Chinese people.
A few deceased ago, a beautiful blue gemstone was discovered in the African country of Tanzania. The stone, named after the country where it was found, is called tanzanite. It can be a clear blue, violet-blue, or bluish purple. The richer the color of the tanzanite, the more valuable it is. Pure blue or rich violet blue stones are the most valuable tanzanites. Tanzanite is also pleochroic.
Source: Gemological Institute of America