Tag Archives: crossed polars

Sliced thin; an unfolding story of sandstone

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derivation of sediment from bedrock, repeating the cycle

What do you think of this analogy; sandstone, and a pile of garbage? I jest, of course. Garbage is no laughing matter – it has become a defining environmental issue of global import. Sandstones too are not to be sneered at.

Your pile of refuse will consist of the flotsam and jetsam of a lifestyle – things you no longer need or want, things acquired over time from any number of localities, some of which may be very far away. Garbage anthropology is a thing. Enlightened folk examine piles of old rubbish because they provide data that allows them to decipher lifestyles and cultural norms.

Sandstone is a sedimentary rock made up of a collection of grains; these too accumulated over time and could have been derived from sources close by or very far afield. Grains of sand Continue reading →

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Sliced thin; time and process recorded in igneous rocks

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This is the second in a series on the geological world under a microscopeThin section of olivine undercrossed nicols showing a kaleidoscope of interference colours

Geologists, it seems, are never satisfied with just looking at rocks from a distance; there is some innate need to wield their pointy geological hammer. Break that rock; give it a good bash! To the uninitiated, this may seem a bit pugilistic, a kind of primal wonton destruction. But a good geo won’t hit rocks just for the hell-of it; a good Geo will be selective. Most of my field assistants and post-graduate candidates needed to be reminded of this. Find something of interest? Before you do anything else, sketch and photograph it; no one will be interested in looking at photos of rubble.

Looking ‘inside’ rocks serves a unique purpose; it allows you to travel back in time, to picture the ancient world, ancient events, outcomes of processes that involve the benign and the brutal, terrifyingly beautiful. Rocks contain memories of all these. And that is why we sometimes break them apart. The optical, or polarizing microscope allows us to unlock these rock memories in a uniquely visual way.  Continue reading →

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Sliced thin; kaleidoscopes with a geological purpose

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This is the first post in a series on the geological world under a microscope

As a kid visiting my Scottish grandparents, I would make a bee-line for two delights in their house (after the hugs); the kitchen (following my nose) to the inevitable trays of homemade donuts and shortbread, and the living room credenza wherein was kept an old kaleidoscope. It was a triangular prism (most modern forms are tubes), filled with glitter, two mirrors at one end, and a peep-hole at the other. This simple toy introduced me to the world of symmetrical, kaleidoscopic, never-repeated patterns.  Years later, as a geology student, I was introduced to optical mineralogy, the science and art of identifying minerals under a polarizing microscope – flashbacks to my childhood. Continue reading →

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