I had been looking at thin sections of banded iron formations, an important source of iron ore. According to Wikipedia
"Banded iron formations (also known as banded ironstone formations or BIFs) are distinctive units of sedimentary rock that are almost always of Precambrian age.
A typical BIF consists of repeated, thin layers (a few millimeters to a few centimeters in thickness) of silver to black iron oxides, either magnetite (Fe3O4) or hematite (Fe2O3), alternating with bands of iron-poor shales and cherts, often red in color, of similar thickness, and containing microbands (sub-millimeter) of iron oxides."
We have a piece of BIF in our garden. I collected it on a geology field trip to the Upper Peninsula of Michigan many years ago. Here it is:The thin section I used as my working diagram contained banded quartz, hematite, siderite and riebeckite. Here was my first try:
|QMSR#1, 20" x 26"|
|QMSR#2, 26" x 27"|
|QMSR#3, 7" x 10"|