Beautiful Spessartine Garnet Schist...

[storm]

Found this earlier today:

[Janie]

I'm curious as to why you are calling this a schist when it is foliated like gneiss and/or stretched like mylonite? I would like to know how to tell the difference.

[storm]

I'm curious too.   

I really don't know what to call this type of formation.  But I've posted these photos on a Geology Forum and hope they can give me some insight.  I'm hesitant to call it a gneiss because of the yellow bands (likely Spessartine--I've had similar yellow material tested by a lab).  It does remind me of the banded quartzite we have around here--here's a photo of the Spessartine Garnet:


Here's pink Rhodonite with clear-ish Quartz, black Manganese Oxide and yellowish Spessartine:


Here's pink Rhodonite bands in Quartzite:


All of these have been identified by Cannon Microprobe Laboratory in Seattle.

I found a reference to Spessartine occurring in Gneiss:

"Hawley Formation (carbonaceous schist facies) (Middle Ordovician)
Gray, rusty-weathering, fine- to medium-grained, generally layered schist and granofels, composed of quartz, oligoclase, and biotite; some muscovite and graphite, rare garnet and kyanite or sillimanite. Layers of quartz-spessartine rock (coticule) common."

We have nearly all of those minerals around WW...

[storm]

I think this rock meets the definition of gneissic on Wikipedia.

Man, I could spend all week on the Internet looking up things related to our local rocks and minerals (and still not really understand anything...).

[storm]

I did find this photo of pink Spessartine with Magnetite blasts (specks) on the same site as the Forum I post questions on:

http://www.mindat.org/photo-38883.html

[storm]

Some geologists have suggested to me that they consider these specimens to be gneiss...