Below are shown ten typical bases that I use for gem trees. By far the most popular and most used are the quartz crystal bases. Most bases will be from 3"X4" to 8"X8" and 1" to 3" high. The availability of some bases is limited.

Amethyst	Selenite
Quartz Crystals	Smoky Quartz Crystals
Fluorite	Drusy Quartz
Geode	Petrified Wood
Barite with Calcite	Galena, Sphalerite, and Dolomite