I googled something the other day and I thought I saw something saying that a dwarf is < 10 earth masses. Huh. Did you find that somewhere?
I like the classification... but I don't think there will be many rock giants. You may also need to make a more firm dividing line... Give some densities. 2.64 g/cm^3 is silica... So maybe 3 g/cm^3 and higher would make something a "Rock"y planet, rich in iron, silica, and other metals like nickel and cobalt.
Ah. I've found something.
Gas Giant page on Wikipedia:
Planets above 10 Earth masses are termed giant planets.[1] Below 10 Earth masses they are called super earths or, sometimes probably more accurately for the higher mass examples, "Gas Dwarfs" e.g. as suggested by MIT Professor Sara Seager[citation needed] for Gliese 581c using a model where that exoplanet was mostly composed of hydrogen and helium. The term "gas dwarf" was also used previously by others.[2][3]
With this terminology in mind, some astronomers are starting to refer to Uranus and Neptune as "ice giants" to indicate the apparent predominance of the "ices" (in liquid form) in their interior composition.[12]
So, if we define "gas" as hydrogen and helium, "ice" as volatiles, and "rock" as metals and either silicates or carbon compounds (
http://en.wikipedia.org/wiki/Carbon_planet), than we have a partial classification.
We can also define transitional states, such as Pluto (transition between ice dwarf and rock dwarf), and hypothetical planets which contain roughly equal proportions of rock and gas, ice and gas, or all three.
Further subclasses could also be defined.
For example, ice dwarfs could include a "wet" subclass, consisting of planets with a well-defined liquid surface (as opposed to a gaseous atmosphere transitioning to supercritical fluid, as is found on most giant planets), and a "steam" subclass, referring to planets hot enough to have their volatiles in gas and supercritical fluid states.
Rock planets would have "oxygen" and "carbon" subclasses, as well as a "lava" subclass for each of those (reserved for planets extremely close to their stars, or moons undergoing absurd amounts of tidal heating.
Gas planets (and possibly ice giants) would use the Sudarsky classes.