Help ID Rock/Mineral

[Bidgee]

This rock came from a stream near Tumut NSW. About as big as a small fist. Dominant lithology is the region is granodiorite. It has an usual mineralisation/structure. I'd appreciate any thoughts on what the structure may be. The images are of the main sample plus a fragment I broke off.

TIA

 

[Martin]

It could be Staurolite or Tourmaline.

 

[Bidgee]

It could be Staurolite or Tourmaline.

I've done a bit research and I think they are some type of amphibole within the granodiorite - possibly hornblende. They are striated and triangular in cross section.

 

[Rusty Pick]

This rock came from a stream near Tumut NSW. About as big as a small fist. Dominant lithology is the region is granodiorite. It has an usual mineralisation/structure. I'd appreciate any thoughts on what the structure may be. The images are of the main sample plus a fragment I broke off.

TIA

Check the cleavage angles, if its 60-120 than its hornblende (amphibole). Tourmaline has a concoidal fracture. Stauralite is mostly a retrograde metamorphic associated with garnet and schists.
As a total guess, I reckon its amphibole formed near the early stage intrusion margin. Its higher up the bowens reaction series, so not late stage fluid crystalisation like a pegmatite. Appears to have a mojority of Na Feldspar and some quartz in there as welle. See if you can find ant twinning planes on the feldspar cleavage with a loupe. There were Tourmalines at Cooma in the road cutting opposite the Metro Roadhouse heading south to Jindi. Part of the Monaro metamorphic and intrision complex...