Wednesday, May 23, 2018


This is me 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.  

One good thing about the volcano erupting on the Big Island of  Hawai'i right now is that its doing something lapidaries love--creating new rocks! 

Unfortunately, most of it will be Basalt, the ugly cousin in the rock family. Basalt is the stuff you see hardened over the current lava flows, but it can hide some lovely secrets! 




Volcanic rocks originate from igneous magma within the earth's crust. When most of us lapidaries think of volcanic rocks, the first thing that comes to mind is Obsidian; that beautiful black/brown glass rock that makes magnificent cabochons.


However. . . Obsidian isn't all that common in Hawai'i. It's only found at the  Pu'u Wa'awa'a Volcano on the west side of the Island of Hawai'i. The current eruptions are at Kilauea, on the eastern side. 


After the Mt. St. Helens Volcano erupted, some clever glass makers created ornaments from the ash, so I decided to find our if the ash or Basalt from Kilauea was good for that. I'm not a glass maker, but I sure enjoy making  cabs from slag glass! 


No such luck, a phone call to Hot Island Glass, a glass studio in Maui let me know that the Hawai'ian  lava Basalt doesn't have enough silica for art glass.



Olivine on Basalt from Hawaii  

There are several lovely minerals found in the Hawai'ian Islands, including Jasper, Sunstone, and Labradorite, but for my money, Olivine is the most interesting.


Olivine can be found in basalt and it is the mineral that can become the gemstone Peridot. 


Island legends say that Peridot is the tears of the goddess Pele. 


Peridot is a 7.0 on the Mohs scale, about the same hardness as Jasper. so it can be cabbed, but the remarkable translucent properties it can have also make it appealing to faceters. It is known as the gemstone for August birthdays. 


The green stone in this ring is faceted Peridot sitting on an Olivine and Basalt  specimen.


A lot of Peridot is found at the Diamond Head landmark in Oahu. It's often called the "Hawai'ian Diamond".





This beautiful mineral is also found in Basalt flows. It comes in a range of colors and translucency's from absolutely clear to milky peach with some browns and reds. When you look at it from different directions, you are likely to see a "spangled" flashing of light.





Labradorite is also formed in Basalt and has been found in the Hawai'ian Islands - although probably not this piece from my collection. 






Travel Tip!

If you get a chance when you're in Hawai'i, try to get by the Papakolea Beach in Mahana Bay where the sand is green because of all the tiny Olivine crystals found there.

No less dramatic are the black sand beaches (Basalt sand) found on several islands. This sand is formed when the hot lava falls into the ocean and explodes from the temperature difference and is ground into ever smaller pieces by waves.


That's all for today. Until next time, I'm your Lapidary Whisperer, 












Wednesday, May 9, 2018

Breccia or Conglomerate? Enquiring Minds Want to Know!


For me, the fun thing about brecciated or conglomerate rocks is the way they tend to tell stories. The image at the top looks like a landslide with the larger, heavier pieces crushing the smaller ones as it rolls forward. Or maybe it's wood (although it's not) logs resting on smaller material.   
 While I'e found that the terms "brecciated rocks" and "conglomerates" are often used interchangeably in the field  to cover rocks that are formed by bits of rock being held together by a matrix, I discovered that the two names are kissing-cousins in the rock world. 

Technically, breccia is a sedimentary rock that is made up of broken  sharp clasts (bits) that weathered off the main rock. They can be found at the bottom of the formation or have moved in a debris flow. These clasts are bound together in a  that may or may not be the same material as it is compacted to form this new rock.
Some minerals, like sandstone.granite can form breccia completely of their own material when the larger bits are compacted in with mineral grains. Breccia formed with multiple types of  are clasts referred to as polymict breccia.
This cool looking brecciated combo rock is definitely not jasper or agate. The bits caught in the black material are also the pink and apparently broke off it before being contained in the black.about 5.5 on Mohs scale for both colors.
Obviously, these pictures are not to scale, but you can see that this brecciated rock made a lovely cab.


When the bits that weathered off the primary rock have gone a distance and have had their sharp edges rounded by water or the action of a debris field, you have a conglomerate.Some beautiful ones occur when the clasts are held together in a matrix of quartz or calcite. Of course, most of us see an example of a man-made conglomerate every day--concrete.

This cross slice from a large conglomerate jasper/agate rock has smoother edges and a bit of white agate that brightens the look. I know some people make clocks out of slabs like these and this one would be a natural since it already has a natural void in the center!

This one has wonderful colors and the brecciated bits are softly rounded and could be mistaken in some areas as a moss. It's primarily jasper with white and clear agate matrix.You know it's near my dinner time, because I'm seeing a red and yellow pepper salsa over a sour cream-filled burrito..
I fell in love with this brown and clear conglomerate jasper/agate because I can see all the way through it at some points because the agate is so clear.



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Until next time,
Your Lapidary Whisperer