Ehhhh.
Well ....
I'm not expert but I've read quite a few books by people who are experts (some who are and some who might be so-called...)
TAKE THIS AS A STARTER COURSE WITH A TEACHER WITH LIMITED KNOWLEDGE - PLEASE CORRECT AS NEEDED....
Well, for starters, just looking to see how the orientation of an agate nodule in its formation - look for uruguay lines (waterlevel lines) to give you a clue. Those are what you see at the bottom of this nodule from Acton CA:
Or this geode/thunderegg from Potato Patch - Wiley Well District
Sometimes the rock shifts via earthquakes between the times agate is set down and two (or more) bands show different planes of formation. (Has a term for them but can't remember right now. Tilted...no...eh...)
Anyway - if there is no waterline (uruguay) banding, then you're stuck (at least from me). Agates formed inside pockets are said to form by a certain process - but this is still being argued...
1 - hollow pocket is lined by minerals
2 - hollow fills with a silica solution
3 - somehow banding occurs (or not) depending on conditions, existing minerals in solution, other conditions.
Now (A) happens
If hollow is completely filled, (several ideas) the agate may start crystallizing on the outer husk until filled -- or the whole nodule might harden and the banding form during this process. (Agate being cryptocrystalline quartz - microscopic crystals) forming nodules without much color (Turtle Mountains)
or tons (Agate Creek)
If there is not enough solution to fill an agate completely, then the agate (cryptocrystalline) will shift creating normal quartz crystals in the center:
Acton
Hauser Geode:
Then - if there is not enough solution to completely fill the hollow, geodes form:
Tiny hollow - Acton
Larger Hollow -
Rainey's Well - Bradshaw Trail - Wiley Well District
Now - in the hollows, when filled with the silica solution - crystals can form in any direction - so I don't know if you can take those stalag thingys as clues to directionality of formation.
OR they show that the solution moved downward creating those stalag thingys over a bed of smaller quartz crystals forming in the silica pool below.
But I may be wrong. There may be a third or fourth or fifth theory.
Sorry for reading my post - especially if you prove my thoughts wrong...! Please fix them for others (and myself) if I am way off base with what I am saying...
And Jim - if I said anything you already know - I duely apologize.
I just felt like posting pictures of random stones...
Lowell