Wednesday, February 5, 2020

Chrysoprase and Little Green Apples

My Chrysoprase

The apple-green color caught my eye and the brown threads going through it impressed me.  It was being sold by the gram, which normally is a no-no for me, but I couldn't resist.  The seller had a few sample cabs of the material and they were story-worthy and very shiny!  So he got to play with my credit card for a minute and I got to take home a chunk of the talkative Chrysoprase! 
Bing Image  Gemmy Chrysoprase

Before I saw this, when I've thought of Chrysoprase,  I've thought of the gemmy variety. Chemically, Chrysoprase is a cryptocrystalline chalcedony  that contains nickel giving it its green color in a variety of shades.

It can often be found at serpentine deposits.

Depending on where it is mined, it can also be called  Australian Jade, Chrysophrase or Jadine.


Bing Image  Chrome Chalcedony

While the color in this mineral is from nickel, there are other green rocks and minerals that get their green from copper, iron, chromium, or manganese. Sometimes, chrysoprase is confused with Chrome Chalcedony which is colored by chromium.

Back to chrysoprase.  The best place for me to find it is at rock shows 😏  It comes to them from mines in California, Brazil Indonesia, Western Australia, and north-central Europe. 


Working the material was a dream.  A good dream (yes, we all know rocks that have turned out to be nightmares - I'm talking to you apatite). To me, this looks like a powerful need plants have to grow up from their roots to freedom.

At between six and seven on the Mohs scale, chrysoprase is a firm rock, and I start it on the 80 grit wheel to do the rough shaping so it doesn't take forever. The next two wheels get the shape smooth and it's ready to polish.  Since it is a fairly hard rock, I take my time on the three polish wheels to be sure I get the best result.  On my Genie, I have a 50,000 wheel that gives a glass-like polish. The cabochon above actually is a combination of gemmy (the dark green which doesn't show it here, but is translucent) and not-so-gemmy chrysoprase.

Chrysoprase from Western Australia

As you can see, the material I purchased (at the top), It has random brown lines through it, making me wonder what stories were lurking behind them. I forgot to ask the vendor where it came from, but seeing this picture of the mineral from the Yerilla Chrysoprase Mine in Western Australia, I suspect it may have come from there

All this has gotten me thinking about other gemstones that may not be all that gemmy.  Check in next month to see what I learned about "gemstones" that are better on the grinding machine than the faceting machine.

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Until next time,

Your Lapidary Whisperer




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
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.

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,