Birthstone Information

DECEMBER:
ZIRCON,
LAPIS LAZULI,
TURQUOISE
and, recently, TANZANITE

Zircon is crystalline zirconium silicate, a natural stone which should not be confused with the popular diamond simulant "cubic zirconia," which is crystalline zirconium oxide--a synthetic gemstone.

Colorless zircon has the distinction of being one of the few natural gemstones that has dispersion ("fire" to the layperson) that aproaches that of diamond, and was extensively used as a diamond substitute before the advent of cubic zirconia.

Zircons have a Mohs' hardness of 6.5 to 7, and are brittle--very prone to nicks and scratches. Most ring stones that have been worn on a regular basis for a year or so will show severe abrasion on the facet junctions. My recommendation is that these stones be used for pendants and earrings, or as a stone in an occasionally worn ring, in order to prolong the useful life of the gemstones.

Zircons come in most colors--red, orange, brown, violet,blue, green and yellow, as well as the colorless variety mentioned above.

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Lapis-Lazuli is one of the few gemstones that is actually a "rock" (a combination of several minerals), as opposed to most other gemstones, which consist of a single mineral. The main ingredients are lazurite (blue), calcite (white), and pyrite ("fool's gold") which provides the gold flecks.

Lapis has a uniform massive, sometimes granular appearance, with a strong blue color, occassionally with a hint of violet. The presence of white patches of calcite or spots of pyrite reduce the gem's value, as does a violet overtone (this according to one authority--another equally respected authority states that a violet overtone enhances the value...I guess that it depends on whether or not you like the violet overtone...)

Lapis-lazuli has been used since ancient times, both in jewelry and in making art objects. With a Mhos' hardness of 5 to 6, great care must be taken to avoid scratching the surface of lapis.

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Turquoise--the name literally means "Turkish stone," due to the fact that it was first brought to Europe by Levantine traders, generally known as Turks. The best (and fairly rare) quality of Turquoise is deep blue, uniform in color, and contains no matrix inclusions. Just below this in value is fine quality "spiderweb" turquoise which has a thin lace-like pattern of matrix throughout the stone. The value of turquoise decreases as the amount of included matrix increases.

The more desired sky blue color will change into dull green by heating. An undesirable change in color can also be obtained through the influence of light, contact with perspiration, oils, and cosmetics, through contact with chemicals (including salt water and swimming pool chlorine), and through the loss of its natural water content. Note the green color of the nugget in the picture--the dark blue stone in the ring was cut from the inside of this nugget--exposure to natural elements degraded the outside skin color.

Turquoise is somewhat soft--5 to 6 on the Mohs scale--but is relatively compact and wears well. Turquoise, like lapis-lazuli, has been used since ancient times, and is believed to be the earliest stone used in jewelry--a mummy has been unearthed that places its use as early as 5500 B.C.

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Tanzanite was first found in 1956 in the Merelani Hills of Tanzania (well, obviously, it was found long before that, but not brought to the attention of gem dealers until then). This is the only place in the world that it occurs because, as was determined later, the Merelani Hills are actually Merelani Crater--formed by a prehistoric meteoric impact upon a specific mix of minerals. Tanzanite is the crystalline form of the mineral zoisite, and has a hardness of 6.5 to 7--this means be careful not to scratch it when worn in rings (Valley Jewelers' custom designs generally are made to give this stone a lot of protection). This stone is generally recommended for use in pendants and earrings.
Tanzanite in its natural state has three colors, depending which axis of the crystal you are observing--blue, violet, and straw yellow. All commercial tanzanite has been heat treated to change the yellow to blue, thereby creating a beautiful cobalt blue stone with violet highlights.
In recent years, this stone has been added to the official jewelers' birthstone list as an option for December.

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