20 pounds of Montana arrived on my porch

I'll show you and others the dud pile sometime.  I first picked out nodules that interested me.  Then, I windowed a whole lot of them, separating those that still interested me after seeing inside.  Even after high grading twice, once I really start cutting them less than half are worth slabbing.  Other times, I slab a whole nodule, and after washing off the oil, I can see a bunch of fractures that were well hidden by the oil.  

Much of my rough is small (1/2 to 1 pound nodules), so it's not a terrible loss then they are duds.  I have had better luck getting good quality smaller nodules, since the good, big ones are high graded out before they ever reach me.   

Even worse than the pure duds are the nodules with great patterns, but lots of fractures.  I have a hard time abandoning a nodule with great patterns or dendrites.  So I cut, reposition, cut, reposition, etc, trying to find some little solid areas the size of a preform.  Sometimes I cut up the whole nodule and end up with nothing but a bunch of very small tumbling rough.  

I've read that 20% of the agate nodules from the Yellowstone produce good slabs (good patterns + solid enough).  Seems about right in my experience.  That makes is expensive rough.  But like you say, you don't need them all to be good.  Two or three good, decent size nodules will probably provide more Montana agate preforms than you feel like cabbing in the near term.  

I'll keep my eye out to see how the other ones look inside, and I'll post a photo of my dud pile (100+ pound) when I get a chance.  

stardiamond

When it comes to MT agates...

1. No matter how well healed a fracture looks, if I can feel it with my fingernail, it will probably break when cutting the preform or when cabbing.

2. Most inclusions / moss / color in Montana agates comes from an ancient fractures which allowed iron or manganese to leech inside.  Most such fractures are not well healed.

3. The "best" inclusions / patterns (those usually not indicative of fractures) were created as the agate formed. They usually have two related forms:

A. Round (or pom-pom or leafy) black dendrites, and

B. Brown or black ribbon banding or concentric banding.

There is a clear relationship between the two (dendrites and banding). The dendrites often form in the shape of bands or occur alongside bands.  These bands follow the original botryoidal structure of the agate, although this is only obvious when cut at certain angles.  

Here are "good" inclusions that didn't form from fractures.  




This nodule is a fascinating example.




It is no accident that the best MT agate cabs are usually one of those patterns -- dendrites, bands, or bands + dendrites.   I see few good cabs full of the healed-fracture type inclusions since they are rarely solid.

This type of inclusion is beautiful but almost never solid.  



You are more experienced than me with the joys and sorrows of MT agates.  But others may find my observations interesting.   

85mm width.

Display Base is 35mm to show relative size. These were all cut directly from the rock. I need to glue the cut remainders to boards before slabbing.


I sorted the rough and these came from the lesser box:

Crazy enough, I know of an area right outside of prineville on a private ranch that has material that is dead ringer for Montana agate. Now.. not all the material is like what you posted. Most just has bands or random dendrites throughout. However I have found chunks that look like what you posted. It’s just crazy to me that the same conditions that form material, can happen miles and states apart an produce similar material. Nice slabs by the way. Those are extremely nice.

I'm away from home base and don't have access to the nice stuff, however, I did find these two pics of large chunks in my phone. Thought you might enjoy. Most of the pieces at the area are big chunks like this. But the smaller golf/tennis ball sized chunks have better pattern and more bands dendrites etc.