Know Your Gemstones: Onyx & Tanzanite
Whether they’ve been coveted since ancient times or only discovered within the past 50 years, gemstones are as valuable or collectable as they are beautiful. In this “Know Your Gemstones” blog series, we’re bringing you the history, science, and lore behind some of the most beloved stones. This week, we’re looking at onyx and tanzanite.
Catch up on this blog series – Click here for Part I: Carnelian and Tiger’s Eye, click here for Part II: Chrysoprase and Lapis, click here for Part III: Moonstone and Turquoise, or click here for Part IV: Amber and Jade.
Ancient Onyx
Disk Brooch with Cameo. ca. 600 (mount); 100–300 (cameo). Langobardic (mount); Roman (cameo). Sheet gold, onyx, glass, and wire. Via metmuseum.org.
Onyx derives its name from the Greek word “onux” meaning “claw” or “fingernail.” The name “onyx” was originally used to describe a type of marble (with white and yellow veins) which resembled fingernails. According to legend, the goddess Venus was asleep on the banks of the Indus River when Eros cut her fingernails with an arrowhead. The clippings fell into the sacred river, sinking to the bottom where the gods turned them into onyx.
When we think of onyx, however, a black stone comes to mind; not the white/yellow marble of ancient times. It’s interesting to note, though, that onyx also comes in white, reddish brown, and brown varieties. “Sardonyx” refers to a variety of brown onyx with white and red bands.
Onyx is typically identified by its black base and white upper layer and banding. This banded stone can also technically be identified as an agate. It is formed by “…the deposition of silica in gas cavities in lava, which results in the distinctive bands or stripes we see in the stone.”
Pure black onyx is rare and, since ancient times, onyx has been dyed to change its color to the desired ebony hue. To achieve this, the stone is soaked in a sugar or honey solution and then heated in sulfuric acid. This carbonizes the sugar, creating a black color.
Like the opal, onyx has the connotation of being a gem of misfortune and sadness:
Despite these connotations, onyx has been coveted since ancient times. The Romans carved it into seals and intaglios. It was prized by Victorians who carved the stone into cameos and mourning jewelry. Today, onyx is typically cut into cabochon and beads used in various jewelry. Small statues have also been carved from onyx. Onyx also serves at the gemstone for the 7th anniversary (black onyx, specifically, is used for the 10th anniversary).
Onyx jewelry should be wiped clean with a moist cloth. Because the stone is so porous, it may absorb chemical cleaners or soap which can cause discoloration. It is also not recommended to use ultrasonic cleaning on onyx jewelry.
The Newest Gemstone, Tanzanite
Tanzanite Earrings. Via http://tanzaniteringshq.com/earrings/.
Tanzanite stones may be 585 million years old, but they only came on the scene fairly recently:
D’Souza thought that he had discovered a new sapphire deposit, but had actually stumbled upon something new and unique. The discovery of this one-of-a-kind gemstone was truly miraculous as tanzanite can only be found at the foothills of Mount Kilimanjaro in Tanzania.
Because tanzanite is so new, there is not much legend or lore relating to it. There are also no synthetic varieties of the gemstone either.
Tanzanite enjoyed an explosion of popularity in the 1960s and 1970s due to a large publicity campaign by Tiffany & Co.. Tiffany named the stone after its limited geographic origin – Tanzania. Though the beautiful gemstones are simply a blue specimen of zoisite, Tiffany believed that “tanzanite” was a much more exotic and attractive name than “blue zoisite.” Tiffany’s campaign was successful and tanzanite’s desirability soon rivaled that of the “Big Four” (diamond, sapphire, emerald, and ruby).
Tanzanite is a pleochroic gem, meaning that it will appear to be different colors depending on how you view it. Some tanzanite stones will appear blue when viewed head-on, but appear purple or red from other angles/directions.
Only the rarest of tanzanite gemstones are naturally blue in color. However, heating the stone to 600 degrees Celsius for approximately 30 minutes will improve the color. It will also convert brown or green zoisite into the beautiful blue stone.
A relatively soft stone, tanzanite only rates a 6.5 on the Mohs Scale. It is vulnerable to chips and scratches with daily wear and use. It is also sensitive temperature changes. “Tanzanite is best suited for earrings, pendants, and other jewelry items that will not encounter abrasion and impact. It is less suited for use in a ring. Many jewelers recommend that “tanzanite rings are for dress rather than daily wear.””
Tanzanite should be cleaned carefully with soap and warm water. It should never be cleaned with an ultrasonic cleaner (which can cause irreparable damage).
Sources
Main image: Onyx Earrings. Via https://www.viauestatejewelry.com/product-page/antique-victorian-onyx-and-pearl-drop-earrings
Guide to gemstones – https://www.wixonjewelers.com/education/gemstones/gemstone-guide/
The Gemstone Onyx – http://www.minerals.net/gemstone/onyx_gemstone.aspx
Onyx Symbolism – https://www.gemsociety.org/article/history-legend-onyx-gems-yore/
Onyx Meaning, Powers, and History – https://www.jewelsforme.com/onyx-meaning
Onyx Gemstone Information – https://www.gemselect.com/gem-info/onyx/onyx-info.php
Tanzanite – https://www.gemselect.com/tanzanite/tanzanite.php
Tanzanite – https://geology.com/gemstones/tanzanite/
Tanzanite Description- https://www.gia.edu/tanzanite-description
Tanzanite History and Lore – https://www.gia.edu/tanzanite-history-lore
Tanzanite Meaning, Powers, and History – https://www.jewelsforme.com/tanzanite-meaning
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