Solar System Matter

It is useful to simplify the more-than-100 elements of the periodic table into the following four catgories.
Rocks are mixtures of little grains of relatively pure chemical substances called minerals. You can write a chemical formula down for a mineral, but you almost always have to write many chemical formulae to describe the content of a typical rock. The most common rocks are silicates such as SiO4 and lots of closely related oxides of silicon, aluminum, and magnesium. Rocks on earth come in three basic families. And we add "primitive rock" to the list for rocks that have never melted or been significantly altered (and therefore cannot have been part of earth, originally, since earth started molten).

Differentiation is an important word in planetary science. It refers to a simple idea: what if you had a molten planet. The densest material would naturally fall toward the center of the planet, while the fluffiest material would naturally buoy to the surface. So one would get a planet that is chemically different from core to surface, i.e. differentiated. Our earth is layered, starting from the core, metal - heavy rock - light rock - hydrosphere - atmosphere. Is it just a "planet thing?" No, big asteroids can also differentiate.

Basic composition of the outer solar nebula in either gaseous form (H and He), or little solid grains:

Material Percent by mass
Hydrogen 77.0
Helium 22.0
Water 0.6
Methane 0.4
Ammonia 0.1
Rock and Metal 0.3