If you have even a very inexpensive wet saw, you can make a very creative mirror "frame" using marble or slate. In our mountain cabin, we had an entry that really needed a nice mirror. At Home Depot, I purchased a 24 X 36" plate glass mirror (no bevel) and glued it to the wall of the entry way, using 8d nails into the drywall beneath the mirror to support it until the glue dried.
The following day, I bought and ripped some slate floor tile that matched the colors of a fireplace in an adjoining room. I ripped the 12" slate tiles into 1", 2" and 3" pieces and then began surrounding the mirror with them, cut to random lengths. I began with the 1" surrounding the mirror, using Liquid Nails as the adhesive and straight pins to hold the slate pieces onto the drywall until the Liquid Nails set. Making sure no seams were the same, I then moved to the 2" pieces using the same technique, followed by the 3" ones. That gave me a 6" surround, which looked just fine.
No attempt was made to grout any gaps and the slightly rustic look of the irregular seams was perfect for what I wanted to do.