![A translucent rock on a postcard creating a magnifying optical effect next to a small jar of black sand with a magnet stuck to it](https://pbs.twimg.com/media/ED9dINgU0AANHI5.jpg)
Which means you can use it to visualize magnetic field lines. Ooooooh, pretty!
![](https://pbs.twimg.com/media/ED9iNKWUYAA4Ap8.jpg)
(Yes, any time anyone asks about my banded iron formation jewelry, I tell the story of stromatolites.)
Get real-time email alerts when new unrolls are available from this author!
Twitter may remove this content at anytime, convert it as a PDF, save and print for later use!
1) Follow Thread Reader App on Twitter so you can easily mention us!
2) Go to a Twitter thread (series of Tweets by the same owner) and mention us with a keyword "unroll"
@threadreaderapp unroll
You can practice here first or read more on our help page!