Worm-like grooves on Cat Spur Creek Almandine

Hello all!

The pic is of an almandine garnet from Cat Spur Creek, Emerald Creek Area, Shoshone County, Idaho. Many of the garnets from this location have this characteristic "worm-like" appearance on the surface, many of the "worms" filled with limonite. The "worms" are in the surface layers only and do not go all the way through. I tried looking these up, but couldn't find any info...

Does anyone have a suggestion as to what causes the "worm-like" surface features? Could it be dissolution? Fracturing?

Thanks,
Jen

Jen,

The garnet looks as if it has crystalized against another mineral which was originally partly embedded in the surface. Later this mineral which may have been a mica, has been dissolved or removed by erosion leaving crevaces that can may have been filled with secondary disposition of goethite precipitating from circulation water.
Knut

could it have anything to do with the snowball metamorphic textures? I think thats something if i remember....

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A buena hambre no hay pan duro

I don't know what a snowball metamorphic texture is. What Knut says makes good sense.

Thanks folks, but a couple more questions....

Knut, would the other mineral theory work for the majority of garnets in the deposit as the "worms" are characteristic for the site... I'm guessing the original matrix would be a schist as schist is the matrix rock at nearby Garnet Gulch. I think Cat Spur Creek is an alluvial deposit so that would work to wear away a mica for sure.

Matt, I've never heard of the snowball texture - do you remember any more?

Thanks,
Jen

Hi,

Snowball garnets are rotated garnet porphyroblasts with spiral inclusion trails.

-Mike K.



Edited 1 time(s). Last edit at 11/08/2009 06:47PM by Michael Kieron.