In planetary science

Planetary science

Planetary science is the scientific study of planets , moons, and planetary systems, in particular those of the Solar System and the processes that form them. It studies objects ranging in size from micrometeoroids to gas giants, aiming to determine their composition, dynamics, formation,...

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

Volatiles

In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...

.

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, asteroids in the inner belt. A fraction of the mass of other asteroids, giant planets, their moons and Trans-Neptunian object

Trans-Neptunian object

A trans-Neptunian object is any minor planet in the Solar System that orbits the Sun at a greater distance on average than Neptune.The first trans-Neptunian object to be discovered was Pluto in 1930...

s is also made of refractory materials.

Classification

The refractory elements

Chemical element

A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. Familiar examples of elements include carbon, oxygen, aluminum, iron, copper, gold, mercury, and lead.As of November 2011, 118 elements...

 can be divided into several categories:

• the super-refractory having condensation temperatures higher than 1700 K (Re, Os, W, Zr and Hf);
• refractory with condensation temperatures lying between 1500–1700 K (Al, Sc, Ca, Ti, Th, Lu, Tb, Dy, Ho, Er, Tm, Ir, Ru, Mo, U, Sm, Nd and La);
• moderately refractory with condensation temperatures from 1300 to 1500 K (Nb, Be, V, Ce, Yb, Pt, Fe, Co, Ni, Pd, Mg, Eu, Si, Cr);
• moderately volatile with temperatures in the range of 1100–1300 K (Au, P, Li, Sr, Mg, Cu and Ba);
• volatile—700–1100 K (Rb, Cs, K, Ar, Na, B, Ga, Sn, Se and S) and
• very volatile—less than 700 K (Pb, In, Vi and Tl). This temperature is close to the condensation temperature of troilite
  Troilite
  Troilite is a rare iron sulfide mineral with the simple formula of FeS. It is the iron rich endmember of the pyrrhotite group. Pyrrhotite has the formula FeS which is iron deficient...
  
   (FeS).

All condensation temperatures are under pressure of 10⁻⁴ bar

Bar (unit)

The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...

. However, slightly different groups and temperature ranges are used sometimes. Refractory material are also often divided into refractory lithophile

Lithophile

Lithophiles are micro-organisms that can live within the pore interstices of sedimentary and even igneous rocks to depths of several kilometers....

s and refractory siderophile

Siderophile

Siderophile means "iron-loving". This can refer to:* Siderophilic bacteria, bacteria that require or are facilitated by free iron* Siderophile elements, chemical elements such as iridium or gold that tend to bond with metallic iron, as described by the Goldschmidt classification* Siderophilia,...

s.