Short answers, pulled from the story.
In planetary science, refractory refers to any material with a relatively high equilibrium condensation temperature. These materials, which include metals and silicates, are contrasted with volatiles, which condense at lower temperatures.
Super-refractory elements have condensation temperatures at or above 1700 Kelvin. Elements in this category include rhenium, osmium, tungsten, zirconium, and hafnium.
Condensation temperature is defined as the temperature at which 50% of a given element exists as a solid under a pressure of ten-to-the-negative-four bar. Scientists note that slightly different groups and temperature ranges are used in some contexts.
The terrestrial planets and the asteroids of the inner belt are composed primarily of refractory materials such as metals and silicates. Giant planets, their moons, and trans-Neptunian objects contain refractory materials only as a fraction of their total mass.
Refractory lithophile elements are rock-loving and tend to concentrate in silicate minerals, while refractory siderophile elements are iron-loving and tend to dissolve into metallic iron. This distinction affects how elements are distributed between a planet's core and its mantle and crust.
Very volatile elements are those with condensation temperatures below 700 Kelvin. This category includes zinc, lead, indium, bismuth, and thallium.