So I don't have a script in front of me at the moment, but...
I'm pretty sure when first arriving in 65 million BC (before Lavos' fall), when Crono and company ask about the Dreamstone, Ayla states that there is plenty of shiny red rock everywhere, referring to Dreamstone.
I assumed that this is the red rock that is referenced as being the source of the Masamune, the origin of the Mammon Machine, etc. Especially because, when writing the scenario of Chrono Trigger, the Frozen Flame didn't exist yet as a plot item. I do believe that Chrono Cross sort of retroactively hints that the red rock in Zeal - within the Mammon Machine - is the Frozen Flame.
I also think the two are somehow related, although entirely separate. I think the Dreamstone is moreso "of the planet" and thus is used to forge dreams into reality, ie the creation of Dream Creatures like Masa, Mune, and Doreen. It also clearly has energy conducting/producing properties and was crucial in the creation of the Mammon Machine. The Frozen Flame, meanwhile, is foreign and a planetary contaminant as a piece of Lavos, somewhat at odds with the planet. I think the Frozen Flame has some elemental ability to control and interact with the Dreamstone, and this is why the Mammon Machine (forged from Dreamstone) encases the Frozen Flame when used by Zeal.
Sort of my interpretation. Nothing formally canon, mind you.