Refractory (planetary science)
# Refractory (planetary science)

In planetary science, any material that has a relatively high equilibrium condensation temperature is called refractory. The opposite of refractory is volatile.

The refractory group includes elements and compounds like metals and silicates (commonly termed rocks) which make up the bulk of the mass of the terrestrial planets and asteroids in the inner belt. A fraction of the mass of other asteroids, giant planets, their moons and trans-Neptunian objects is also made of refractory materials.

## Classification

The elements can be divided into several categories:

| Category | Condensation temperatures | Elements |
| - | - | - |
| Super-refractory | higher than 1700 K | Re, Os, W, Zr and Hf |
| Refractory | between 1500 and 1700 K | Al, Sc, Ca, Ti, Th, Lu, Tb, Dy, Ho, Er, Tm, Ir, Ru, Mo, U, Sm, Nd and La |
| Moderately refractory | 1300 to 1500 K | Nb, Be, V, Ce, Yb, Pt, Fe, Co, Ni, Pd, Mg, Eu, Si, Cr |
| Moderately volatile | 1100–1300 K | Au, P, Li, Sr, Mn, Cu and Ba |
| Volatile | 700–1100 K | Rb, Cs, K, Ag, Na, B, Ga, Sn, Se and S |
| Very volatile | less than 700 K | Zn, Pb, In, Bi and Tl |

The condensation temperatures are the temperatures at which 50% of the element will be in the form of a solid (rock) under a pressure of $10^{−4}$ bar. However, slightly different groups and temperature ranges are used sometimes. Refractory material are also often divided into refractory lithophile elements and refractory siderophile elements.

