All three December birthstones are best known for their beautiful shades of blue. These gemstones are among the oldest on Earth. With one of the earliest mined and used in jewelry, to one of the most recent.
December birthstones are relatively inexpensive, but their beauty rivals even the most precious stones. Colorless cubic zirconia is a convincing replacement for the diamond. Also, tanzanite often substitutes for sapphire, while turquoise is unique in its robin's egg blue hue.
Tanzanite
Tanzanite is the exquisite blue-purple variety of the mineral zoisite that we find in only one part of the world. It was so named because of its origin in Tanzania and quickly became popular because of its recent discovery.
Zoisite existed for over a century and a half before the discovery of this rare blue variety in 1967. Small amounts of vanadium, mixed in extreme heat, cause the blue-purple color, from light blue to intense ultramarine with purple tones.
Because of the variety of colours, tanzanite can show different colours when viewed from different angles. However, it must be properly cut to bring out the more attractive blue and violet hues and to downplay its undesirable brown tones.
Most tanzanites we find on the market today have been heat treated for the few brown colors found in natural ones and the enhancement to the blue shades of sapphire.
Tanzanite is found only in a few square kilometres of land in Tanzania, near the majestic Mount Kilimanjaro. Its price and availability are directly linked to the mines in this region. But most are now slowing production significantly.
Tanzanite has values of 6.5 to 7 on the Mohs hardness scale and is not as hard as the sapphire it often replaces. Given its susceptibility to scratching during everyday wear and abrasion, tanzanite is better suited for earrings and pendants than for rings.
Zirconium
Zircon is an underrated gemstone that is often confused with synthetic cubic zirconia due to similar names and its common use as a diamond simulant. Few people realize that zircon is a striking natural gemstone found in a variety of colors.
The name “zirconium” is probably derived from the Persian word zargun, meaning “golden”. Others trace it to the Arabic word zarkun, meaning “catacomb”. Given its wide range of colours in red, orange, yellow, green, blue and brown, both origins are plausible.
Zircon is usually reddish brown, which can be popular for its earthy tones. However, most gem quality stones are heat treated until they become colourless, gold or blue (the most popular colour). Blue zircon, in particular, is the alternative birthstone for December.
The colour differences in zirconium are caused by impurities, some of which (such as uranium) may be slightly radioactive. These gemstones are also heat treated to stabilise the radioactivity.
While radiation can break down the crystal structure of zircon, it plays a crucial role in radiometric dating. Zircon, the oldest mineral on Earth, contains important elements in the formation of our planet.
Colorless zircon, known as the Matura diamond, displays radiance and flashes of colorful “fire” that can rival the fine diamond. But there is one key difference. Zirconium is more fragile. Although it measures 7.5 on the Mohs hardness scale, its thin edges can shatter.
Zircon from Australia dates back 4.4 billion years ago. Australia ranks first in global zircon mining and produces 37% of the world's supply. Other sources include Thailand, Sri Lanka, Tanzania, Tanzania, Cambodia, Canada and the United States.
Turquoise
It has been admired since ancient times. Turquoise is known for its distinctive color, from light blue to robin's greenish blue. It is one of the few minerals that lend their name to anything that resembles their striking color.
The word “turquoise” dates back to the 13th century, from the French expression pierre tourques, which referred to the “Turkish stone” brought to Europe from Turkey.
Ancient Persia (present-day Iran) was the traditional source for the heavenly blue turquoise gemstones. We often call this color “Persian blue” today, regardless of its origin. The Sinai Peninsula in Egypt was also an important historical source of turquoise gemstones.
The US is now the world's largest supplier of turquoise in the world. Nevada, New Mexico, California and Colorado have produced turquoise, but Arizona ranks first in production in value as well as quality. The popularity of the stone here makes it a staple in American Indian jewelry.
Turquoise is found in arid areas where rainwater dissolves copper in the soil, forming colourful nodular deposits when combined with aluminium and phosphorus. Copper contributes to the blue hues, while iron and chromium add a hint of green.
Some turquoises contain pieces of the central rock, called matrix, which appear as dark webs or patches in the material. This can reduce the value of the stone, although the uniform “cobweb” pattern of southwestern turquoise is attractive.
Turquoise is sensitive to direct sunlight and solvents such as makeup, perfume and natural oils. The hardest turquoise measures only 6 on the Mohs scale, which has made this soft gemstone popular in carved amulets throughout history.
From the ancient Egyptians to the Persians, Aztecs and Native Americans, kings and warriors have admired turquoise for thousands of years. It adorned everything from jewelry to ceremonial masks, weapons and reins. Highly regarded for its striking namesake colour and ancient history, turquoise's popularity remains timeless
