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Anonymous: Hey, could you maybe tell us about Labradorite? I checked wiki but I don't understand half the words there. I'm not a giant rock fan, but I like cool rocks and Labradorite looks really cool. Sorry to bother you!
Okay, so, Labradorite. Labradorite is complicated and sciencey, as all good rocks are. I’ll see if I can explain it in a way that makes any sense! (Once again, I’m not a scientist! Correct me if I’m wrong!)
Most minerals, when they’re bright and pretty and colorful, look like that because while they were forming some impurities got mixed into them - usually metals like iron, copper, or titanium. Without any impurities, these rocks would naturally be colorless. We call these guys allochromatic (other-colored).
Other gemstones are certain colors because those elements are an important part of how they formed. They’re not impurities that got mixed in, they’re actually part of the gemstone. Their natural color IS the color you’re seeing. We call them idiochromatic (inherently colored).
But labradorite doesn’t get its color from either of those things. Labradorite is special. It’s part of a third group: psudochromatic (false colored). These rocks aren’t colorful at all, but they LOOK that way when light passes through them.
See, labradorite is actually just… grey. From most angles, it looks like this:
You have to look at labradorite from a pretty specific angle to get those flashy colors, so when we cut it into cabochons for jewelry, or just polish up big pieces of it, we’re careful to do so at the most flattering angle, the angle that shows the most schiller, or “those cool glowy colors.”
Why just the one angle? It’s all about labradorite’s crystal structure, and how it’s formed.
Labradorite is a rock that cooled down really slowly. Because of that, it’s made of lots of very very thin layers of crystal, stacked on top of each other and all pretty much aligned in the same direction. These are alternating layers of albite (mostly sodium), and orthoclase (mostly potassium), which solidify at very slightly different temperatures. Labradorite is a rock that cooled in just the right way for a thin layer of albite to form, then a thin layer of orthoclase, then another thin layer of albite, and so on.
When light hits labradorite at the perfect angle to pass through a bunch of these layers, you get the schiller effect. Basically, a little bit of the light gets bounced off the first layer and back to your eyes. The rest of the light passes through to the second layer, and a little bit gets bounced back to your eyes again, and so on. Every time more light gets sent back to you, it’s a little out of sync, and this makes it look like a different color.
(This is a very simplified way of explaining this.)
If these layers were all perfectly the same size, you’d get a uniform color, like the blue in moonstone. But in labradorite, these layers might be different widths in different places, so different parts of the stone will reflect back wildly different colors! We call this effect labradorescence to differentiate it from the uniform colored adularescence found in moonstone and some opals.
Depending on where it’s found in the world, labradorite can reflect all sorts of different colors!
But whatever color it is, Labradorite will always be the Best and Coolest Rock.
Look what I’ve got! A little pebble of sunstone! Sunstone is a feldspar mineral, related to moonstone and labradorite. It’s well known for its glittery shine. That glittery optical effect is called aventurescense, and it’s caused by light shining off of a bunch of teeny tiny metallic inclusions, such as hematite or copper.
If I put this sunstone pebble under my microscope, we can suddenly see these inclusions! They form as blade-like crystals inside the feldspar, all facing the same direction so the light catches them at the same angle. A tiny, shiny stone!
Dun Briste and the surrounding cliffs were formed around 350 million years ago (during the ‘Lower Carboniferous Period’), when sea temperatures were much higher and the coastline at a greater distance away.
As a fun little addition, look about a third of the way up, where the clean horizontal lines of the outcrop are broken by a small arc, thick in the middle and pinching out towards the sides, concave upwards and with a darker/black color.
That’s a fluvial deposit, probably a small creek or river- the arc is a cross section, so the lowest point is the deepest part of the river. It’s darker because it was rich in organic matter, and after the plant matter was buried here the constituent carbon remained for millions of years- possibly as a small lignite or coal deposit. (‘Carboniferous’ period, right? It’s a common sight in this age of rock)
This is a 350,000,000 year old riverbed. Fun to imagine standing by that ancient creek, ferns and primitive moss growing thick in the shallows, insects and the odd critter enjoying themselves on the banks, and knowing that something of this moment would remain even three hundred and fifty millions years in the future, embedded in a monolith rising above the sea.
“Baikal Zen”: Rocks that have fallen on the ice of Lake Baikal are heated by sunlight and emit infrared rays that melt the ice below. Once the sun is gone, the ice becomes solid again, creating a small support for the rock above.
scrolling down I was like “oh what a cool idea! someone skipped stones on a lake and took high speed photographs to get these pictures where it looks like the water is holding up the stone which is kinda was does happen a-oh, no. nope. it’s just Fucking Lake Baikal up to its god defying nonsense again”
Most materials used as gemstones are minerals that grow as single crystals, preferably transparent and with strong colours. A few are not, organic gemstones such as amber and coral (now prohibited under the CITES treaty) are one obvious example, but here we are going to discuss a unique rock with an interesting geological history formed by a chain of geochemical circumstances. Some people have given the name mineraloid for stones of this sort, but I’m not convinced.
