Basics
Fireplace crystals can be purchased online from several major manufacturers. The crystals are compatible with vented, gas fireplaces that use a manual key valve to control the flow of gas. The companies also sell a custom burner designed for use with the fire crystals, but you can use your own if you already have one. The crystals do not emit soot or ash, so your fireplace will not require constant cleaning.
Installation
Before beginning, make sure the fireplace gas is turned off and that your fireplace is clean of soot and dirt. Next, you'll install the special burner that comes with the crystals; it screws into the valve at the side of your fireplace. Test the burner to make sure it works before you cover the floor of the fireplace with the fire crystals. You can stack the crystals however you'd like, using whichever colors you prefer.
How It Works
The glass fireplace crystals -- which can be handcrafted or tumbled -- trap and retain heat without melting or crumbling. They are heated up by the flame generated by the burner and absorb the heat due to their high reflectivity. Because the crystals don't actually burn, they will last a long time and do not need to be replaced frequently. Additionally, the manufacturers guarantee that the crystals will not lose their color.
Other Considerations
When deciding how much of the crystals you'll need, you will have to measure the dimensions of your fireplace. Generally, you want to cover the floor of your fireplace with at least 3 to 4 inches of fire crystals. If you have a propane-powered fireplace, you will need to buy a special pan burner to avoid a potential explosion. With fire crystals, you don't have to have a fireplace screen -- unless you have kids or pets -- because the crystals don't throw off sparks.