Archaean Banded Iron Formations (BIF's)

Ah gemmaruby,

Excellent question! the fine grained quartz comes from god taking a big dirty shite during the Archean! The big dirty shite was then converted to chlorite about 4 million years later by the great mystical creature who goes by the name of disco kev, master of the house, king of beers and THE beer legend. You will never know where the master of the house will turn up next but rumour has it he will be in the roost tonight at 10 o'clock if you would like to ask him yourself.

Hope that helps!

Hi gemmaruby, the coarse grained quartz was the original silica band laid down and as it was not fully solid upon deposition the finer grained material is where the silica band was further compacted as the BIF was forming. As a matter of fact this phenomenon has little to nothing to do with the bowel movements of God our saviour.
Happy Geology!!
ps you should notice undulous exitinction in your thin section which indicates strain

Thanks very much for your help!

Actually professormcdavies, thats not entirely correct. Although indeed the silica band would not have been solid, this would have no effect on the grain size during compaction as said "strain" would only be responsible for any UNDULOSE** extinction seen.. the areas at which the quartz is in contact with the iron band should have finer grained sio2 as the iron-rich minerals such as magnetite or hematite will inhibit the growth of sio2, hence why the larger grains are seen the further away from the iron banding. hope that answers your question gemmaruby.

Thank you very much!

westenrivers, who do you think you are? I think you will find that compaction does effect grain size. Perhaps your brain itself is lacking in Haemoglobin

It's a topic where a bunch of sock puppets are all talking to each other.