Blue Agate Crystal

This is a slice of blue agate crystal, which our son bought for me as a present when he returned from a school trip (I think to Germany) when he was about 15 years old. 
I use it as a coaster at the side of my bed. It's very pretty, and has shades of very delicate blues, with turquoise and white layers.  This central section that I have shown here is quite small. The hole is about 2 cm at its longest point (I've just had my ruler out!). 
I thought this would do nicely for the Tiny Tuesday Challenge this week, as the subject is "Mineral".  
Thanks to Thisislife for hosting this week's challenge.