This is one of my favorite rocks.
It looks boring on the outside, but it's awesome on the inside.  It is called a Geode.  I got this at my favorite Rock Shop, Earth, Wind, Fire & Ice.
It is located in Chadds Ford at the Pennsbury Antique Mall in Pennsylvania.

This Rock from my collection is called Mica.  It breaks easily, so if you decide to collect Mica, make sure you keep it in a safe place. 

This is called Pyrite, also known as Fool's Gold.  It looks like the gold that jewelry is made from, but it isn't.  It's a lot cheaper that real gold and looks nice in a rock collection.

IGNEOUS ROCKS

Igneous Rocks are formed by the cooling and solidification of magma.  This may occur at the surface (volcanic rocks) or at varying depths within the crust (plutonic rocks).  Igneous rocks are commonly identified by mineral content and texture.  Plutonic rocks are slow cooling and, consequently, have large crystal size and a coarse grain.  Volcanic rocks are rapid cooling and produce a small crystal size and a very fine grain.  Numbers 1-8 are Plutonic, 9-15  Volcanic.

(Copied from the box the rocks came in...)

1. Pegmatite	2. Granite (coarse)	3. Granite (fine)	4. Gabbro	5. Granite Porphyry
6. Syenite	7. Diabase	8.  Diorite	9. Amygdaloidal Basalt	10. Basalt
11. Rhyolite	12. Lava	13. Pumice	14. Scoria	15. Obsidian