In a paper published this week in the journal American Mineralogist, a team of... American mineralogists, came up with a new classification system for rare minerals. It turns out that out of more than 5,000 known minerals in the world, more than half of them are considered rare.

And I hate to break this to you if you're into more conventional jewelry, but stones like diamonds and rubies don't even qualify.

If there is enough of a mineral out there for it to be sold commercially, it's not actually rare, geologically speaking. But the researchers determined four criteria that should be used to decide whether a mineral should be considered rare.

The first is whether a mineral forms under unique conditions, like the mineral hatrurite, which you'd think would be pretty common because it's made of calcium, silicon and oxygen, all pretty easy to find on Earth. But hatrurite only forms when it's hotter than 1250°C, so it doesn't show up in many places.

The second way a mineral could be considered rare is if it's made of elements that you'll hardly ever find in Earth's crust, like beryllium. In its pure form, beryllium is a light, shiny metal, but it doesn't occur in its pure form in nature, it can only be found when it's paired up with other elements, like in the gemstone known as beryl.

Then there are minerals that might form often enough but don't stick around for very long. Methane hydrate crystals, for example, will just dissolve in air at standard pressure.

The final category covers minerals that come from places geologists simply don't visit very much, like the insides of erupting volcanoes or the deepest parts of the oceans. Plenty of minerals fall into one of these categories, but some qualify for more than one, and for a few minerals, all four of these criteria are true.

A mineral called fingerite, for instance, forms from copper, oxygen and vanadium - an element that is relatively rare in minerals - and it dissolves in water. You know, like, whenever it rains... It also comes from fumaroles - dangerous holes near active volcanoes that spit out hot gasses, so the conditions that form fingerite are both rare and difficult for geologists to access.

So, if you're shopping for a gift this Valentine's Day that's really rare, give the gift of fingerite. 

But let's say you aren't ready to give each other rare, exceptionally dangerous gifts. Let's say you're happy spending time just staring into each other's eyes, or, just planning on spending this Valentine's Day hanging out with friends and family.

Well, a paper published this week in a journal called Trends in Cognitive Sciences has some advice for you. A group of social psychologists analyzed studies that looked at the way we mirror each other's physical expressions, what's known as "sensorimotor simulation". Like, if your significant other has a particular way of crinkling their eyes when they smile, you might find yourself doing that too.

But the psychologists found out two weird things about this sort of simulation. First, when you make a facial expression, like a smile of a scowl, it can trigger your brain to make you feel the emotion associated with it, like happiness or anger. The second thing they noticed was that to understand expressions on other people's faces, we make those expressions ourselves.

So, according to the researchers, you might not be mirroring other people's expressions on purpose, but that's your brain's way of figuring out what they're feeling. Essentially, your brain is trying on the expressions  it sees on other people and seeing how they make you feel.

The idea is that if smiling - or scowling - in the same way as your friend or your crush makes you happy or nostalgic or angry or sad, then you'll have a better idea of what they're feeling.

So the next time you're hanging out with... anybody, keep an eye on their facial expression. If you notice them mimicking yours, they probably aren't just copying you, they're trying to understand what you're feeling. And, maybe, they're even into you.

Thanks for watching this special Valentine's episode of SciShow News, and thank you especially to SR Foxley, out Patreon President of Space. If you want to help us keep making the show, you can go to patreon.com/scishow and if you want to keep getting smarter with us, you can go to youtube.com/scishow and subscribe!