Friday, July 5, 2019

MARIPOSITE - LAPIDARY WORTHY?

My Mariposite yard rock.

The green and white that make up Mariposite make it an attractive yard rock. But as they say in the television commercials, there's MORE!

WHAT'S IN A NAME?

When miners during the California Gold Rush discovered they could find gold and placer gold in the green and white rocks around them instead of standing in a cold creek with a pan, they named the rocks Mariposite for the town they were standing in. (Not a huge imagination happening here, but a great way to tell others where to find it).


It can be found in many areas around the world, where it is mostly called Mariposite, except for Canada where they call it Virginite for some reason. Now, if you want to check my research, please check for Virginite on Google. When I checked on Bing, their articles under "virginite" were not about rocks. Nuf said.

WHAT IS MARIPOSITE?

It's actually not a mineral. Depending on how you want to think about it, it's either a metamorphic rock or a conglomerate. Chromium-rich Mica give the rock its green color and its flash. Dolomite Marble or Quartz provide the matrix. 

Mariposite slab



CAN I CAB IT?

 That depends on your willingness to handle disappointment. First, let's examine the hardness on the Mohs scale of the mineral which compromise the rock

Mica       2.5-3 
Dolomitic Marble  3.5-4
Quartz  7

As you can see, the Mica and Marble are similar in hardness, but soft as heck. If you want to cab it, plan on making it into a pendant where the edges are encased or it won't last long.  When the Mica is next to Quartz, undercutting is a real problem. 

I decided to create some Mariposite flowers for this blog post. Not my best idea ever. You can see that  I got one (of several tried) flowers. The plan was to make three and make a divot in the center that would hold a crushed yellow rock/epoxy mix to make it look like a flower. 

Flower start in Mariposite 


The first one came out fine. A bit rustic, but that was what I was looking for.  The others, even though I was using 220 grit and higher, shattered. Apparently, this rock is known for, basically, falling apart. I plan to try to get some more done so I can make a flower arrangement, but I think I'll need to drop them on the floor first to see where the slab breaks naturally.

OTHER USES

Aside from gold mining and cabs, Mariposite has traditionally been used for other practical purposes including being a facing stone for buildings or fireplaces and even markers in cemeteries (although I suspect they weathered so quickly that their messages were soon lost).

Have you worked with Mariposite?  What was your reaction?

Until next time, your Lapidary Whisperer,

Donna








 

Wednesday, June 5, 2019

Onyx or Not?

Green striped Onyx lapidary slab
When I was thinking about a topic for this post, I noticed a slab of onyx on my worktable. The pastel green layers were beautiful, and still are, but now I know it's not really onyx.

Darn.

It's still a lovely material, but it's one of those situations where it's a lot catchier to call a mineral Onyx, than Banded Calcite.

The banded calcite, CaCO3, is a carbon-based mineral that is commonly found in Mexico and India. From a lapidary standpoint, it's pretty soft at around 3 on the Mohs Scale. 




POPULAR DECORATIVE MATERIAL

Onyx bowl in browns






Like me, you may have a bowl, carving, or chess set made with this soft stone. The softness of this material also means when you start working it on your grinding wheels, it is best to start with your second wheel in so you don't take off too much material too quickly.








Mindat.org Onyx image




 TRUE ONXY is actually a variety of Agate, and as such, hits the Mohs scale between 6.5 and 7, making it more than twice as hard as banded calcite. According to Mindat.org, Onyx is a black and white banded agate or at times a monochromatic agate with light and dark bands. It does come in brown and red varieties; they are called Sardonyx. Mindat states, "Agate and onyx are both varieties of layered chalcedony that differ only in the form of the bands: agate has curved bands and onyx has parallel bands." The stones with parallel bands have been used to make cameos.


Now, bear with me.  In the Mindat.org image, I would have just called this banded agate even though the brown layers are somewhat translucent. They are parallel, but also curved.  Of course, translucence is not a requirement of Onyx. In fact, it seems to rule the material out.
Wikipedia Onyx image


Now, the more I get into this, the stranger it seems. Here's another image from Wikipedia they claim is onyx. 















Limestone Onxy
According to Mindat.org, there are a lot of stones called onyx, like this limestone onyx(CaCO3).

Checking around the internet, I found claims of green onyx (can be one of several items), onyx opal, rhodochrosite onyx and more. It seems as if any mineral that is translucent is being labeled onyx. 



GETTING REAL

Under the theory that "IT IS WHATEVER I SAY IT IS" I hereby declare that in America, Onyx is a translucent calcite. It is very soft. It has layers, most often parallel, and comes in a wide range of mostly pastel colors. The GIA might disagree with my declaration, but since they don't include Onyx as a gemstone in their online Gem Encyclopedia, well, my decision stands. 

WORKING THE SLAB



The slab at the top is the one that inspired me to do a blog on Onyx. So, of course, I had to work on some of it. 

I know the picture makes it look somewhat cylindrical, but it's not. I cut across the light bands and domed it, making the straight lines look like they are curved. From one side to the other, the back is flat. I played around with the top so that it is flattened in a way that mimics the curve in the rock making the picture a bit of an optical illusion. Then I put a bevel all around the back edge to keep the material from chipping.

Fun stuff!







I'd love to hear what you think on this topic. 

Until next time,

Your Lapidary Whisperer,

 Donna
 









Finely Banded Black & White Onyx