One suggestion, with regards to how to make crystal clusters into wire jewelry, is to use a minimal amount of wire so the focus remains on the featured material. In the picture here, you see a silver-dollar sized amethyst crystal cluster made into a pendant I titled Vineyard Harvest. The cluster reminded me of grapes, so I mixed half hard and dead soft 20-gauge square wire for the simple frame (carefully entwining the softer wire between crystals) and accented it with Bali silver leaf beads. (The modified frame is based on my Anything Pendant Harness.)
Of course, you also should take into consideration the back of the crystal cluster, the geode matrix. If it is very rough you may want to make a woven, open mat-style frame from round or square wire for the back first (or crochet the backing) and then attach the cluster as described above.
Answer contributed by Dale "Cougar" Armstrong