I'm hearing good things about Azomite, but my understanding is that it is a trademark name for rock dust mined in Utah. Now for my money, Utah seems a long way to truck anything heavy, not to mention the word "mined" sticks in a sore spot.
Trace minerals, volcanic rock, aluminum silicate....
Volcanic sediment is often touted as great source of fabulousness. I think Lorax mentioned it relative to the Ecuadorian soil and I think that's part of the Japanese Akadama and some other black mud (that I can't remember the name of) mystique for Bonsai. I'm sure that is true.
For me, greensand is a more local source of trace minerals but I don't think there is anything volcanic about them and the mineral composition is marine sediments and closer to other marine sources like kelp. I'm trying to find a comparison study/chart.