Everything is relative! I did some research for you:

• Perlite weighs 5-20 lbs/cf
• Pumice weighs 40 lbs/cf
• Granite weighs 100-170 lbs/cf

The ranges probably depend on whether the rock is solid, broken or crushed as well as other factors such as where it is from. Hope this helps.

Thanks! What I lifted felt like more than twice the weight of perlite - it was a bit surprising. Maybe it was just that brand though. It’s puzzling. There is a farm supplier around here, I guess I’ll just go buy and feel up the merch.

I appreciate the answer though.

Pumice is a lot heavier than Perlite. There is a variation in bulk density depending on the source. Also Pumice will absorb more water than Perlite will and so a wet mix will be even heavier.

Are you doing a roof garden?

Pumice is heavier than perlite, but relatively speaking, it's not a heavy element in a potting mix. For cactus and succulents it's a delightful ingredient in one's mix, a superior part of it, and many folks use it by itself to reroot plants. A mix of 100% pumice, while very lean, would have to be watered and fertilized often.