Deciding on this week's Partial Ellipsis of the Sun topic was harder than usual. The genetically modified organisms (GMOs) we saw on the western side of Kaua'i, guarded by several people, trucks and barbed wire, was an option. I decided that topic needed more research than driving past miles of corn (in various developmental stages) where sugar cane and pineapples used to grow ten years ago and reading a few articles. I will also read Frankenstein's Cat: Cuddling up to Biotech's Brave New Beasts by Emily Anthes before addressing this topic. (Great suggestion, Jan).
So...deadlines to deadliness :-), on this Tuesday I decided to write about petrographic thin sections because they are something I know and they are amazing beautiful.
Here's a piece of olivine, a magnesium iron silicate (called peridot when of gem quality):
Amazingly beautiful, right? How about cutting a nice, clean, thin slice of this and attaching it to a glass slide. And then, how about looking at this thin slice of rock (or thin section) under a petrographic microscope? Still not impressed?
Well, how about under crossed Nicols filters (see below) under a petrographic microscope, in thin section?
The two polarizing filters on a petrographic microscope work similarly to polarizing sunglasses. Each filter allows light vibrating at one particular orientation to pass through. One of the two filters is fixed. The other can be moved in and out of the light path. That filter's polarizing direction is perpendicular to the fixed filter.
If you put a thin section of a rock in between the two polarizing filters (referred to as looking at the section under "crossed Nicols") it creates the stunningly beautiful portraits we see above of olivine and below of zircon:
The uncrossed filter photograph of zircon, a nesosilicate, is below:
Here's one more crossed Nicols thin section of basalt, a fast-cooling, fine-grained volcanic rock from Thailand with two large spectacular olivine crystals in the center.
And, for completeness, a sample of basalt:
I will end this week's illustration-rich blog with a photo of one of my favorite thin sections of gabbro, coarser-grained (i.e. slower cooling), intrusive igneous rock found near mid-oceanic rift zones (under crossed Nicols):
The brightly colored orthopyroxene crystals are surrounded by striped plagioclase feldspar. Slower cooling produces some amazing crystals.
Stained glass: made by nature.
Enjoy! Next stop, a field trip to Iceland to see the mid-Atlantic ocean ridge on land to see that basalt and gabbro up close!