Sunday, January 5, 2020

Aloha! Hawaiian Treats!


I just got back from spending Christmas week in Hawaii and was once again amazed by the rock formations and lush landscaping I saw there!

This is me six years ago holding up the side of a lava tube at the Thurston Lava Tube also called the Nahuku in Volcanoes National Park on the Big Island.  I'd been hoping to do it again, but I was told that you can't do that lava tube anymore, it's under the recent lava flows. It is a reminder to all of us not to wait to get out and see the natural wonders of our planet. They may seem like they'll be there forever, but changes are always happening--and we never know where or when.

When I was in Hilo, I visited the Lyman Museum (look for a review of it in an upcoming Rock & Gem). Not surprisingly, it features some volcanic materials.

The museum displayed “volcanic bombs” from eruptions. These are composed of basalt. When the liquid is shot into the air, it comes together, twists around, and falls to earth. The shape tends to be oval, like a football. The bomb may be solid or hollow and they are collected as oddities for their shapes and textures.



Volcanic Bomb at Lyman Museum

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Pele's Hair from Lyman Museum
Volcanic bombs and small sharp black splinters are not the only interesting form that falls from the eruptions. There is also Pele’s Hair, Pele’s tears, and spatter. The hair is formed when lava is flying through the air and it stretches because it’s still molten. The resulting thin strands are glass and they sometimes have a droplet at the end. Some call those droplets Pele’s Tears. Frankly, Pele's Hair looks a bit like the hair I take out of my hairbrush; silvery gray with a touch of brown.

Another formation that is called Pele’s Tears is the peridot crystals that can form in olivine. The spatter is exactly what it sounds like, bits of lava that fall to the ground.
NO PLACE FOR LAPIDARIES

Olivine with a few Peridot crystals
The Hawaiian Islands are fascinating for many reasons, especially the chance to see geology in action! It does have some minerals that lapidary artists and mineral collectors look for, but they are largely in microscopic amounts of labradorite, feldspar and plagioclase. The one you’re most likely to find is olivine. Olivine is a green mineral that has very little silica and a lot of magnesium and iron. It is the least stable mineral on the earth’s surface; when olivine gets weathered, it pseudomorphs into iddingsite.  While olivine is a mineral because it has an identifiable crystalline structure, iddingsite passes through many phases of change and so it is referred to as a rock, not a mineral. When the olivine is mixed with pyroxene, it becomes peridot.

Lapidaries have been known to work with basalt when it is dense enough. It will be black and probably have visible dots of other minerals in it and take a nice shine. Because basalt can be light and fluffy as Scoria and goes on a scale to very dense, it doesn’t have a Mohs scale number.  

Full disclosure: Some of the information in this blog post appeared earlier in an article I wrote for  Rock & Gem Magazine. I took the pictures of the Volcanic Bomb and Pele's Hair at the Lyman Museum where I took a whole lot of pictures for the upcoming R&G article.

Show Season is in full swing now. Don't miss the chance to see and acquire amazing specimens, slabs, and rough!  Send me a picture of your favorite!

Until next time, Your Lapidary Whisperer,

Donna



Thursday, December 5, 2019

Cotton Candy Agate for the Holidays?

BECOME A ROCK SHOW VENDOR?  See my article in the December issue of Rock & Gem Magazine! 

When I first saw a slab of peach and white cabbing material, I thought it looked like a sweet confection; then I saw its name, "Cotton Candy". It fit.

Then I showed it to an older rockhound, who authoritatively told me it was "Youngite". Being a curious sort, I decided to find out if they were one and the same thing. Frankly, I thought it was likely they were, but appearances can be deceiving.

YOUNGITE

Youngite (SiO2 ) For many years, this was a popular slabbing material that was not terribly hard to find even though it was only mined in one place inside the Youngite caves near the Glendo and Guernsey reservoirs in Guernsey, Wyoming. The  online expert on this stone is Mike Nelson, I got my information from him personally and his blog site, check it out: Click Here

Mike says  Youngite is a brecciated reddish-brown to peach jasper that was then re-healed by deposition of cream-colored chalcedony.  Often the entire rock is then covered by druzy quartz crystals.  At one time Youngite was fairly common on the market as collectors were able to pull numerous specimens “off the walls” in Youngite cave(s) and voids near Guernsey.  He says he understands that the caves are in the Guernsey Limestone and the breccia clasts are actually derived from the limestone.  


Image Credit: Midat.org





This image shows the common exterior with botryoidal  drusy quartz coating. The quartz portion is fluorescent, which is the quickest way to discover whether you have true Youngite. The Cotton Candy stone is not fluorescent, even though it often looks the same.



Credit: Mike Nelson






Unfortunately, the area where the Youngite was mined is  reported to be mined out and the specific area is no longer open to the public. There are some pieces available, generally at a pretty high price point. If you're considering investing in some, I suggest you ask the seller for regular and short-wave pictures from the same angle to be sure you're getting the real deal.

COTTON CANDY

When I described my Cotton Candy slab and told him I believed it came from Mexico, that explained a lot of the differences between the two similar rocks.  Most of the agate in that part of Mexico comes from volcanic rocks like Retaliate nodules rather than sedimentary limestone like Youngite. The brecciated materials in both probably get their color from iron in them.

So, they really are very different rocks. 


IN MY SHOP



I purchased this slab as "Cotton Candy" at a local rock show.  As you can see, it's pretty dirty and my impression was that it was quite weathered, which turned out to be true. The colors changed dramatically when I worked with it.
My finished cab from the slab above,

You can see the pencil marks I made around the void that has the druzy coated botryoidal shapes and that I used to set the shape.

After I got it cut, shaped, and polished, you can see the yellow-looking matrix has become white with a touch of blue tinge.  The peachy material has finished out as pink and there are obvious bands around the void and the pink. It took a lot of scrubbing to clean the interior shapes, but it was worth it.




My Youngite cab






I had purchased a small slab of Youngite years ago without knowing what it was, and made a cabochon with it. How do I know it's Youngite and not Cotton Candy?  It's fluorescent! 

Youngite contains chalcedony and quartz, so it fluoresces mostly green. I tried my teardrop cab above under the long and short wave lights, but nada. That was a real surprise since the botryoidal formations inside the vug appear to be quartz druzy, but they obviously aren't.

To see how Youngite lights up, check out the image on Mindat.org at Click Here.


Also, when you look at the two cabs, you'll notice how very similar they are. But, a very close examination of their mineral components shows that they are not the same thing at all. Sort of like green gemmy faceted stones. Are they apatite Ca5(PO4)3(Cl/F/OH) or are they emeralds
Be3Al2(Si6O18)? The only way to know for sure is to consult a gemologist.

From a lapidary standpoint, I feel that both materials are excellent lapidary material. They are nice to work with and take a beautiful polish. I would caution about what I noted earlier. Because of its current rarity, real Youngite commands a relatively high price in the market.  Cotton Candy is commonly available. If you are considering a purchase, be careful you get what you pay for.

Until next time, I hope  you find joy (and great rocks) through the holidays you celebrate this time of year.

Your Lapidary Whisperer,

Donna