Rubble rock is made of the broken pieces of the LR
that occurs during shipping. It is the same as LR
, just in very small pieces suitable to be used in a sump or other small space.
Dry rock is just that. It was once LR
(though that may have been many, many years ago) that has been out of water for quite some time.
Marco rocks have always had the reputation of coming loaded with dead tissue in/on the rocks (trapped organics) so the rock had to be cured before going into an existing tank. I see they are now pre-curing the rock before shipping.