I guess this would qualify as a unique rock type.
But like everything else about this stone, it depends on who you're talking to.

Tiffany Stone, or Bertrandite, is also sometimes called "Purple Opal" and "Ice Cream Opalite"
Bertrandite Opal Tiffany Stone would be a good all inclusive name for the material,
but let's just call it "Bert" for short.

Seams of Bert have only been found in the Brush Wellman beryllium mines
located in the Sevier Desert of the Topaz-Spor Mountains of western Utah.
Occasionally some of this material escapes the crusher and makes it way to the surface.
The Bertrandite is the creamy white areas, and the purples and blues are fluorite.
The black lines are mostly Manganese.
Also in the mix are Chalcedony, Dolomite, and Rhodonite.
But the "whole mess" is said to be "opalized".
There you have it.
I have been cutting some Bert rough lately to have some slabs for Grassy Creek!

Now, since I know you all are sitting on the edge of your seats
waiting to see close-up pics of that vug in the Bert
here are a few.
(If nothing else they are colorful.)

This is some very unique material and well worth study.
There is a clear crystal coating over most of the interior of the vug.
The vug is pretty deep going atleast another inch back into the rough nodule.
Here is a series of pics gradually zooming in on the same area
ending with a pic of what looks like a "coated" baby blue fluorite.

With all the reflection it is hard to see the surfaces clearly.
Looking for the "stepping" of fluorite, dolomite, or calcite,
or any other form of calcite.

Wow, cool vug.  Interesting you mention the tiffany stone.  While in AK a couple of weeks ago, I stopped by a cool store in a really neato town of Hope, AK.  Saw the most beautiful cab pendant ever and it was a tiffany stone.  I had to have it.  Had everything I love going on in it.  Purple, green, tree looking lines in the picturesque way the cabber cut it.  The stone speaks and the cabber listened.  Maybe if I figure out how, I will post a pic but don't hold your breath, I'm the queen of good intentions.  Nice stone there, Joe!

Here are a couple cabs I finished recently.
The one on the left is 2" long and 1.25" wide.
The one on the right is very freeform and has a hole drilt in it.
Now anyone familiar with the finicky crazed brittle nature of Bert
will tell you you're crazy to try and drill a hole in it.
So I guess that answers that question.

Joe they are really beautiful.  That is wonderful material.

Well, it is a beautiful and unique stone/rock, to say the least,
and it only took me 4 years to get around to working up another batch.

So I slabbed up a 5 lb piece of what I consider to be real pretty high quality classic Tiffany Stone so I could have some slabs to sell and a few to work with. Unfortunately, probably due to the mining process getting it out of the ground, the piece was riddled with mini-fractures everywhere. I cannot sell a single slab from the lot because, if mailed, it would arrive in multiple pieces.
Here are a few pics of the slabs anyway, for the record.

Here's an end slab from another piece I didn't know what to do with so I polished up one side and stuck it in the Etsy store.
It does have a nice little vug. Vugs are good things.