We Were Totally Wrong About How This Mineral Formed

When you’re browsing the shiny stones  in your local museum gift shop,  

there’s a few staples you can expect to find.

Pointy white quartz crystals, purple  amethyst, shiny golden pyrite, and this:  

layered brown tiger’s eye, winking at you  with its classic cat’s eye reflection.

Since these stones are like,  

everywhere, you might assume that we know  everything there is to know about them.

But it turns out that for over a century,  

we were completely wrong about how tiger’s  eye formed, and even what it’s made of.

Here’s how we got there, and the research  that finally helped us crack the case!

That is a pun that you’re gonna get in a minute.

[♪ INTRO]

Tiger’s eye is the name commonly given to this  gorgeously golden brown banded form of quartz.

What really sets it apart from the other rocks on  the shelf is its silky reflection, which creates  

a line of light moving across its polished surface  that looks like the narrowed slit of a cat’s eye.

It’s a phenomenon known as chatoyancy,  

which is similar to the asterism in  things like star emeralds or rubies.

The stone is made up of ultra-fine fibers,  

all lined up so they catch the light together  and create a single band of reflected light.

That chatoyancy has made tiger’s  eye super popular among collectors,  

and many people carry some around for good luck.

Including our director Hiroka!

But while the mechanics of light  reflection might be well-understood,  

the chemistry and geological history of these  gemstones hasn’t always been so straightforward.

Their story begins in the late 1800s,