Mineral Mondays 56 - Etching Benitoite Crystals

in STEMGeeks7 days ago

Mineral Mondays 56.jpeg

Most people have no idea of the lengthy process between digging a crystal out of the ground and actually getting it ready for the end buyer. In this post I'm going to tell you about one process I do to prepare a rare gem, benitoite, for the buyer.

Before we go any further though, I have to put a warning on this post because this process can put you in the hospital or straight up kill you, no do overs. It's very dangerous and absolutely do not attempt to do what I write about in this post. I have almost 10 years experience in etching crystals and even then I've had 2 instances where I thought I had neutralized the acid only to find out the next day my lungs were in pain and I had a cough for several days. Having said that, let's get into it.

Benitoite

I am going to center this post around the beautiful, blue California State Gemstone, Benitoite. It is an extremely rare barium titanium silicate that only grows crystals big enough for jewelry in a small section of the Diablo Mountains in San Benito County, California. While it's also found in Itoigawa, Japan, Arkansas, and a few other localities in California, the crystals from those localities are too small to be used in jewelry or as display specimens.

Benitoite from San Benito Co. grows on blue & green schist with natrolite, a white crystaline mineral, neptunite, a black elongated crystal and joauquinite, a reddish-brown cubic crystal. The contrast of the minerals produces stunning specimens like this one dubbed "Sushi Plate".

07408680014966245931326.jpg
(Source - Mindat https://www.mindat.org/N2E-F2W)

The crystals above grew when the host rock schist was shattered by hydrothermal forces which also injected the necessary minerals needed to form the crystals, as is the case for many crystals.

Once a piece of blue schist ore, rock containing the minerals, comes out of the ground, through erosion or mining, it needs to be prepared. Here is where we start to get into the second phase of hard work.

IMG_8975 (2).jpg
(Benitoite crystals in rough(unprocessed) above my thumbnail.)

IMG_8974 2.JPG
(It was cold that morning!)

In order to get the crystals out of the matrix the rock has to be etched using acid. In this case muriatic acid, HCL hydrochloric acid, was found to work the best by the old timers. The acid will eat away at the white natrolite leaving behind the benitoite, neptunite & joaquinite crystals.

The solution I use was one recommended by the late John Vreevart on his site http://www.benitoite.com/benitoite/index.shtml. I had met and bought from John many times before he was tragically killed in an auto accident in 2019. His contributions to Benitoite are great. RIP.

IMG_9163.JPG

John's recommended solution was 5-7 parts water, 1 part muriatic acid. Of course you can adjust that a bit depending on where you are in the etching process. Starting out I tend to go a bit heavier with 6 parts water, 1 part acid to etch away a bit more, a little faster. I have to pay attention though and only let the benitoite sit in solution for 1 hour. If you leave it in longer the solution will start to turn to a jelly that makes it harder to clean off.

After each etching I thoroughly rinse the specimen, soak it in a solution with a bit of baking soda for several hours, then let it dry, all done outdoors.

At this point the crystals will start to appear and getting the best looking specimen becomes a challenge. You have to analyze which way you think the specimen will be best presented, which area will show the best sides of the crystals and determine how to create a work of art.

That's really what it comes down to, art, because the area now showing the crystals has to be covered in wax to keep the acid solution from separating the crystal from the matrix. It's a difficult process from here on out because you have to gauge how much of the rock you want to keep with each additional etching. Sometimes you won't get the wax to fully cover and the acid will work it's way in releasing the benitoite. Etching a good specimen can easily take 1 month. Lucky for me I love doing it so the time is not an issue. For many people though they just can't be bothered with this process so you will often see specimens on the market that have etched away all the white natrolite leaving just a benitoite crystal on the schist matrix like this one.

3989d2d594b8909304659001f73736c2.jpg

Ok, so back to the specimen I showed earlier I have been etching for over a week. Here are a few photos of the process starting the day I found it.

IMG_8975 (2).jpg

This is after the fist etching. The benitoites are starting to show so I have to now wax them before the next etching. I also run a shortwave UV blacklight over the specimen to find out if there are any benitoites that I can't see clearly. In this photo the wax is covering the crystal that my thumb was pointing to.
IMG_9030.JPG

The backside. This was promising to see some vugs(hollow areas) because that would give the crystals room to grow.
IMG_9031.JPG

These are from the third etching. New crystals were exposed that weren't visible before. For reference my original, first wax is visible above these crystals.

IMG_9148.JPG

The backside vug had produced 2 more crystals so I waxed them.

IMG_9147.JPG

A nice little joaquinite crystal was exposed too.

IMG_9149.JPG

IMG_9151 2.JPG

At this point I had a problem though. Much of the natrolite was disappearing from around the original crystals and I still had quite a bit of rock to get through, so I decided to do what is a difficult decision, break the rock in half to get at the interior.

Broken.JPG

Unfortunately only a portion cleaved off and there was a large crystal hiding inside.

Broken 2.JPG

The rock split into 3 pieces, all of them having some benitoite. While not a complete loss, it would have been nice to get that single, large crystal exposed in 1 piece.

So now I still have the majority of the rock intact without the center exposed. I could saw cut it or leave it as is and let a customer try his luck at it. I've decided to do the latter. I remember when I was first etching benitoite a great dealer had similar specimens he sold to me as rough. Stuff he didn't want to deal with. So I took several of them, etched them and they became fantastic pieces. Like this, my "nigiri sushi".

IMG_3786.jpg

I still have work to do on that one. I need to clean up the benitoite crystals that have the green schist in them.

Back to the specimen. I melted the wax off with hot water and packed the piece away to take back to Japan with me. While it didn't produce a stunning crystal this time, that is part of the fun working a stone out of the ground, you often times don't know what you will get.

Here are some of the crystals that have been exposed.

IMG_9153.JPG

IMG_9154.JPG

The original crystal turned out to be one of the smaller ones.

IMG_9155.JPG

The two inside of the vug is actually several and could be worked to produce more.

IMG_9156.JPG

The large, broken piece and what it looks like under short wave UV light.

IMG_9157.JPG

IMG_9159.jpg

Who knows, maybe I will get home in Japan and work on it some more. I've got 14days to quarantine so I'll have quite a bit of free time. Maybe I'll pull something out of the center like my favorite piece in my collection. I call it "Gemini", the twins.

Benitoite 2.jpg

Benitoite 1.jpg

Thanks for reading!

Sort:  
 7 days ago 

Oh man, I would have never thought that was a crystal. I probably would have thought the pink stuff was gum stuck to a rock.

The pink stuff is birthday candle wax lol. The crazy thing about this stuff is often times you'll see just a tiny bit of blue sticking out, then open it up and it's filled with crystals. Keep in mind, this stuff is incredibly rare and valuable, but you never know until you work on it. Thanks!

Manually curated by ackhoo from the @qurator Team. Keep up the good work!