is what gave me the idea for this but I didn't have any resistors and didn't want to drive 5 minutes to the nearest hardware store. I didn't actually take any pictures of my work so I got to go with diagrams and a finished product video.
Step 1: What You'll Need
You will need to get the following parts and trust me, it's pretty bare bones. The parts for the light itself can be left up to your imagination. I know I'm going to get chewed out for not using resistors but think about it, rgb led's require voltage range of 3.3-5 volts each (depending on their current color) so wiring 2 in series would require more then 10 volts in order to start to worry and since usb can only carry 5 volts you're definatly safe.
1. 2 5mm rgb color changing led's. You can normally find them easily and cheaply on your favorite auction site.
2. USB cable with a male type A connector on at least one end.
3. Thin wire.
4. Heat Shrink Tubing or Electrical Tape.
5. Hot Glue or Silicone (optional)
1. Lots of rocks with 2 being semi-clear so the led's can shine through
2. Container of your choice
1. Soldering iron and solder.
2. Wire cutters/strippers.
3. Heat gun or similar (optional) if you're using heat shrink tubing.
4. Small metal file and/or drill
6. X-Acto Knife
Step 2: What Do You Want?
This is perhaps one of the most perplexing step and it's unfortunately the first. You have to figure out what kind of container/dish you want your rocks in and decide what kind of rocks you want in it. I used an old mint dish I had lying around and it held all of my rocks quite well. Next you'll want to figure out how you want to position the rocks and where to have the glowing crystals.
Step 3: Wiring
Once you decide what you want you need to have your soldering iron ready. Grab your usb cable and cut it open and strip the red and black wire enough to solder onto, keep the green and white isolated from the other wires because you won't be using them. You'll want to start by soldering the leds together in series, the picture below will explain.
Step 4: More Wiring
Cut a hole in your rock container where you want the usb cord to enter, make it a tight fit because it will look better in the end. Position your led's where you want them to light up your crystals and hot glue them there (optional). Slide your usb cable through the hole and wire red + to the first led + and the black - to the second led -. If you're using a metal container, such as an altoids tin, then you should wrap the wires in either shrink tubing or electrical tape to prevent shorts and ensure long life.
Step 5: Test It Out
Now that you have everything soldered up and insulated, if need be, plug it into the nearest computer and wahlah, magic rocks. If you don't see any light then make sure no bare wires are touching or that you have the led's wired properly. If you get a "USB Hardware Not Recognized" message on your computer make sure the white and green wires are isolated from each other and the other wires.
Step 6: Show It Off
Assuming everything is made as you had planned, or close to it, stick it next to your computer or, if you're like me, plug it into an AC to USB adapter and set it virtually anywhere. I hope you enjoy my little instructable and remember to post pics of your creation in the comments below and show it off to the world.