Mica caps are generally rectangular with color dots. You are correct, most of the time they will be ok.
Those small adjustable caps on tuners are also mica. A sheet of mica is between two pieces of metal.
Norm
:Hi, we don't have to replace mica capacitors in old radio because they are (usally) never bad (see on radio restoration tips web pages)... But what is a mica capacitor? Were are these caps on a old radio? Is it the small plastic piece on top of tuning caps? Thanks!