CLAY & DIRT
For pieces that are heavily coated with clay and mud start with a simple cleaning of warm water, toothbrushes, dental picks, bamboo skewers, etc. Soak the crystals overnight, brush them down and spray them off the next day. Let them dry completely allowing the remaining clay to crack and loosen. Repeat the process until the dirt and clay are removed. Be sure not to use tools that are harder than your material as they may scratch; steel for instance will scratch stone softer than quartz.
Go easy and use light pressure with clusters. They may be attached with only the slightest of adhesion and any pressure will sever that. Some pieces you thought were clusters may even be multiple crystals encased in a single ball of tough clay.
Deep Set Non-Mineral Coatings
If deep set dirt and debris remain after cleaning with manual means; it is time to move up to a more aggressive technique to remove stubborn deposits. This is where our favorite tool comes out! The Textile Spot Cleaning Gun. This device will almost clean rust off of specimens it is so powerful. Use with caution to remove deep set dirt and other deposits from your pieces and let dry, respray if needed. Any deposits remaining at this point call for either chemical treatments or direct mechanical removal.