Blue montana agate

[Tommy]

A close friend just got back from visiting her dad who is an old rockhound living in Montana - with a load of rocks for my gf and I to enjoy. Among the treasures were some chunks of dryhead agate and a large assortment of typical montana nodules. However there was this one rock that caught my eye - it looks identical to a typical river tumbled Montana agate nodule - except for the fact that it's blue - light blue like a baby-blue color all over.

I don't plan on cutting it and will probably keep it as a specimen and maybe polish a side. It's completely devoid of dendrites and it's unusual so I don't see the point in cutting it unless there's a chance of something special inside.

Anyone ever see one of these come out of a batch of Montanas? The photos are pretty accurate with the colors.

[helens]

How odd... the face looks almost like it was used as a cutting/gouging area... those look like cut marks in and around the hole. I can't imagine what purpose that could serve for cutting, so it's probably not it, but it looks like it to me. If for some reason that actually is a tool, it could have been brought to the area from somewhere else.

[Deleted]

I'm thinking it's probably a piece of Madison Blue (also from Montana).

[grayfingers]

This is Madison Blue. I have only seen it as a seam agate.



Here is a Montana nodule with blue, They are rare, I have only found a few.


Helen, what you are looking at is the marks left from the "mold"

[grayfingers]

After finding that last photo, I saw where I had some fun with that shot. . .

[jamesp]

Is the disc/hockey puck mold the same shape in Montana as the discs i find in Texas?
i.e.I guess a lot of volcanic bubble molds are the disc shape asking?

Tommy,i went west to hunt agate(1rst experience w/western agate) and the prettiest were biscuit shaped from molds holes in lava.
No one said why to look for biscuit shaped rocks-i thought they were messing W/me.They had washed down higher altitude lava fields
and ended up in the Rio Grande river.That looks like a typical agate biscuit.You might get a better info source than me.But the same
type biscuits may be near you in Arizona.

Helen,those pocks are from the bubble mold created by gases in lava that later filled w/silicified.We do not have lava fields
like westerners so they assume easterners would know what they are.It was a key method to find which Texas sun bleached pebbles
were pretty on the inside.Moss,plume,dendritic and i think bandeds form this way.I think Brazillian agate ball shaped nodules
are formed in lava bubbles-but round instead of biscuit shaped.

Tommy,i would ask about this if i were living where you do.You need to find out the difference between seam/hillside agate and biscuit/bubble formed if you don't know already.

[jamesp]

Bill,that blue agate is almost as big as you brain but not as dense.LOL
I wish i could do that.

[grayfingers]

James, here is a sampling of nodes from MT rivers. They are usually oblong and flattened, but I have found them round as well.


Here is my 'moon'


Helen, The Montana Moss Agates formed over 65 mission years ago as volcanoes began erupting along the eastern front of what is now the Rocky Mountains. ... For tens of millions of years the harder agates eroded out of the softer basalt. The gas pockets were most common molds, also wood that was encased, making limb casts.

[Bikerrandy]

Avon blue Montana agate. I cabbed some a couple of months ago, really pretty stuff!

[Bikerrandy]

Found it ..... forum.rocktumblinghobby.com/thread/55054

[Sabre52]

*LOL* Now that's an agate! Gray, I love that picture! I've never seen Madison Blue before. That's a very nice shade of blue. Reminds me of Austin Blue agate from Nevada....Mel

[grayfingers]

Never heard of that as a named agate, there is a town called Avon on the Little Blackfoot river, must be from near there.
That is a great cab, Randy!

[Tommy]

Wow that's beautiful Randy, I have suddenly started to question my own judgment in saying I won't cut it hahaha :-) Maybe "just one" exploratory cut today - then that can become the "face" if I decide to keep it as a specimen right?

Thanks for the responses everyone - and Bill, thanks for the moon-shot - It helps keep the size of your nodules in perspective

[Fossilman]

Nice agate! Montana has some outstanding agates there..Have you lighted it to see the clarity???

[jamesp]

No cracks in that cab Randy.Glowish color.Looks like hard material.
Moon??also a bowling ball
Those nodulues seem a little longer than Texas(more like biscuit). the clear agate
i found in Texas are so close to Montana agate its amazing
Here is a typical-does this not look like a Montana???

[helens]

Great thread! I learned a lot, and those are excellent pix Bill, and I remember that cloudy sun cab... it's stunning:).

So... lava holes make gouge marks in rocks and that's what you look for to decide what to pick up when hounding? But I thought all rocks had some types of holes or marks in them from forming? Its very rare to see a perfectly smoothed stone...

[grayfingers]

True Helen, the rounded ones are from the glaciers and the rivers tumbling them smooth. I found another pic of a little guy that is a nice blue, it has a fortification inside, but I had to hold it just so to catch the color which hid the banding.

[grayfingers]

Jun 23, 2013 12:24:41 GMT -5 jamesp said:

No cracks in that cab Randy.Glowish color.Looks like hard material.
Moon??also a bowling ball
Those nodulues seem a little longer than Texas(more like biscuit). the clear agate
i found in Texas are so close to Montana agate its amazing
Here is a typical-does this not look like a Montana???

James, that sure as shootin' does look like a Montana agate! Wow, that is wild.
Bill

[Sabre52]

Yep, the Rio grande gravel has agate that very much looks like Montana agate and I've never heard where those nodules originate from. No one has ever written of clear dendritic agate in situ in Texas or adjacent Mexico far as I know....Mel

[Tommy]

Jun 23, 2013 11:13:12 GMT -5 Fossilman said:

Nice agate! Montana has some outstanding agates there..Have you lighted it to see the clarity???

Yes and as far as I can tell it is very clear throughout. I might go ahead and cut it this afternoon if real life doesn't interfere with my happily rocking.