From the "how did I miss that?" department:
On the phaser rifle page, I point to an example from Insurrection wherein about six cubic meters of rock were explosively disassembled via phasers.
For some reason, I evidently always missed Data's line before that, wherein he identifies the rockface as being a calcite formation.
Calcite denotes the most stable form of calcium carbonate . . . the same stuff you find in chalk, limestone, and marble, and a common fixture in most sedimentary rock formations.
The mineral calcite generally has a density of about 2700 kg/m³. The rockface we see presumably contains various impurities, given that it is not clear or even mostly so as pure calcite would be.
Calcite isn't particularly hard . . . if you catch it just right, your fingernail might scratch it. Because of the softness and other issues, it's difficult to get a fracture out of it.
The shots do not seem to produce significant amounts of molten rock. The phasers produce a firey explosion and physical blasting. If each phaser did a third of the work, then each one would've blasted apart two square meters . . . 5400 kilograms . . . of calcite.
This information can take us toward other bits and pieces, but that will wait for another time.