Hey Patrick –
I think it’s a totally reasonable question, and to be honest, the answer is not as straightforward as you may think! Very coincidentally, I’ve just undertaken a very large project to re-organize the content on IGS, and to also augment certain topics where necessary with comprehensive information. I actually noticed that the Cleaning of Gemstones was a gap in the available information, so I added and edited an article by Gerry Wykoff from our founder Don Clark’s archives. Scroll to the middle of the article and you will find a table that I added which lists stones and stone families, and recommends how they should/can be cleaned or wiped.
Long story short, virtually all gemstones will respond nicely to the careful application of warm water-detergent-soft brush. But there are some that take special attention (see the table in the article). A clean microfiber cloth is more than sufficient for almost all applications.