Card of the Day - Emerald Sphere

If you can't tell from the other card so far this week, I'm a big fan of 0 cost mana artifacts.  This is one a cycle of Spheres that you can sacrifice for a single mana of one color.  The Topaz Sphere (from Monday) is a loose translation of this cycle and got to keep the name.

Edit: updated templating so it works like Chromatic Star.  (thanks, @JVWoodward)