Mineral Mondays #16: Benitoite, The California State Gem
Benitoite
Last week I went over 5 of the rarest gems on earth, one of them being Benitoite. Today I'll be going in depth about a gemstone I know and love.
Benitoite is the California State Gem and a very rare gemstone. The only known source of gem grade material is located in Central California in the Diablo Mountains in San Benito County and the localities where it is found are spread over only a few miles.
The gemstone has a unique shape, high dispersiveness and an uncommon composition. It's chemical formula is BaTiSi3O9 (barium titanium silicate). It's high dispersive property means it can out shine a diamond. It's a member of the hexagonal class of gems and It's ditrigonal dipyramidal crystal class shape is one of a kind among the hexagonal minerals.
History
Benitoite was only discovered within the last 100 years, on February 7, 1907 near Coalinga, California. The gentleman who made the discovery, James Couch, was hired by Roderick Dallas and Thomas Sanders to prospect near the existing New Idria mine which was one of the world's largest mercury producers for the California gold fields.
-note, what is strange is that benitoite was not discovered by the New Idria miners even though they were in the area since the late 1850's. I haven't been able to find any information on benitoite pre 1907. You would think prospectors would have combed the area for other mineral discoveries and reported finding benitoite.
As Couch made his way deep into the Diablo mountains he found a flat clearing and decided to camp for the night. When he woke the next morning he did a bit of looking around and climbed over a hill. On the other side he discovered what he thought were blue diamonds or sapphires littering the ground. Excited, he filled his pockets and immediately went back to Coalinga to inform his employers. The date was February 7, 1907 according to his son.
Source - Collector's Edge
On Feb. 16, 1907 by Roderick Dallas and Thomas Sanders formed The Dallas Mining Company and the mining claims were filed March 2, 1907. What happened next was interesting.
Because of it's shape, color and chemical formula the first few people shown the strange gem did not know what to make of it. Some identified it as obsidian, not sure how someone could do that, and others thought it was sapphire or spinel. It wasn't until it was sent to Sanders' brother, Hal Sanders, in San Francisco whom was a watch maker and jeweler. Hal had passed the gems on to a cutter who sold one faceted piece to a diamond dealer named George Eracet. Eracet knowing it's uniqueness showed it to his friend George Louderback at UC Berkley. Louderback immediately knew it was not a sapphire or a spinel and thought it might be a new species. He urged Eracet to get him some uncut specimens to examine. Eracet went back to San Francisco and obtained some directly from Hal Sanders. He then passed them on to Louderback. Louderback examined them and confirmed they were a new, unidentified species and wanted to examine the locality they came from. After some negotiating with Hal Sanders they made their way down to Coalinga, CA to meet with Thomas Sanders.
When they arrived they were met by James Couch and several other people involved. When they asked to be taken to the mine to study it they were refused by the mine engineer, Leland Hawkings. Luckily later that day Thomas Sander's decided to personally take Eracet and Louderback up to the mine.
During this time George Kunz of Tiffany's in New York had heard about the discovery and wanted in on it. The California group of Eracet, Louderback, Dallas and Sanders agreed to keep Tiffany's at bay until they could finish their field work and give the gemstone a California name. On July 30th, 1907 a report was issued by Louderback naming the stone "Benitoite" after San Benito county where it was discovered.
Despite Tiffany's interest and all the unique qualities benitoite never took off as a commercial gem. While it's still faceted and sold, you won't find it in most jewelry stores. This may be due to lack of supply though.
The Gem
As I mentioned earlier, benitoite is a unique gemstone in the world. It's triangular shape makes it easy to identify. There is a very rare "Star of David" variety as well with two triangles inverse of each other.
It comes in 3 different colors, shades of blue, clear, pink and grey(for stonys). The stonys are a mixture of another mineral called crossite and benitoite. Below is an example of a "stony" gem. They really only have value to the collector as specimens.
Benitoite was formed when hydrothermal fluids rich in sodium were forced into the host rock. Barium leached out from blue schist while the titanium leached out from serpentine and they combined to form the benitoite.
Benitoite comes encased in a white mineral called "natrolite". The only way to remove this from the gem is to use muriatic acid, dangerous stuff. The process is called "etching". Etching a benitoite specimen can take months to process. It just depends on how you want the specimen to appear when finished. It's always preferable to leave a good blanket of natrolite to contrast the blue benitoite though.
I've etched several specimens myself, but I never attempted the final cleaning process which involves a chemical called ammonium biflouride because if you inhale it it will kill you. I know a few chemists who can do this last phase of prepping a specimen so that is how I get mine cleaned.
The gem is often found with 2 other gems, neptunite, a long, rectangular very dark red/brown mineral and joaquinite, a very small, square, brownish mineral.
Another unique feature of benitoite is how it fluoresces blue under short wave UV light. It is unknown what causes it to fluoresce this color! Using shortwave UV lamps is one way to find the gem while hunting for it.
Where To Find It
While only gem quality material is found in California, tiny specimens are also found in Arkansas, Japan and Australia.
The easiest way to obtain benitoite is at a local gem show. Almost every gem show will have a dealer with specimens. The other route is to go up into the San Benito mountains and try to find some. Be aware though, the 4 claims that produced benitoite are still under claim. If you are caught collecting on a claim you can be arrested and in the worse case scenario, shot.
My Collection
I have a lot of benitoite, probably in the range of 20 specimens collected and etched over several years. Each year I add at least 2-3 more specimens. All of it was purchased from John Vreevart and Rick Kennedy, two authorities on Benitoite. Here are some images of pieces I own.
Some Benitoite Facts
- Shape - dipyramidal
- Composition - BaTiSi3O9 (barium titanium silicate)
- Hardness - 6 - 6.5 (medium, diamond is 10)
- Refractive index (fire) - 1.75 - 1.8 (diamond is 2.417 - 2.419)
- Color - light blue to dark blue, clear, pink
- Localities - California, Arkansas, Japan, Australia.
References:
http://www.benitoite.com/benitoite/benitoit.shtml
https://collectorsedge.com/pages/benitoite-gem-mine
http://www.redorbit.com/news/business/1251076/the_100year_history_of_the_benitoite_gem_mine/
Thanks for reading!
Next Mineral Mondays #17: Red Beryl
I do weekly series on Monday, Tuesday and Friday. Here are previous posts for those days.
Mineral Mondays -https://steemit.com/science/@rt395/mineral-mondays-15-some-of-the-rarest-gems-on-earth
Travel Tuesdays -https://steemit.com/japan/@rt395/travel-tuesdays-12-cafe-de-copain-ningen-kankei-cafe-pub-in-shibuya-tokyo
Food Fridays - https://steemit.com/food/@rt395/food-fridays-10-yushoken-ramen-and-izakaya-in-irvine-ca
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Benitoite similar to precious metals.
That's most interesting! Indeed a most unusual shape and I can't imagine that being able to outshine a diamond, it isn't even half as popular as the diamond! Fancy that! Like you said, probably because of its very low availability... A pity, and also a good thing as it makes it even more rare. Thank you for enlightening us! :)
Nice article 😍 followed 😂
✨💍✨😁✋
There is a lot of benitoite for sale in Japan.
The last pic. Has got a lot of purple, when you would clean that, will it become like a purple seethrough crystal? This is a real beauty !!! And most probably the latest one discovered?
It's probably the lighting. Benitoite only comes in shades of blue. It was a difficult piece to photograph because of the tower in the center. The crystals wrapped around it. It was actually two halves that the natrolite had come in and filled in. I was trying to etch it in half, but it would have ruined the specimen so I left it as is. It was my most recent until this past weekend I was able to pick up a few more.
I believe we still have that specimen, but it's listed for sale in Japan right now on our Yahoo Japan shop.
Thanks.
a real gem ! i love it thx for showing !