Refractory
A refractory holds its shape and its strength in a furnace, which is a harder requirement than a high melting point. It has to resist thermal shock, chemical attack by whatever is being melted, and the slow creep that a hot loaded material undergoes — and the material that survives one furnace can fail quickly in the next one along.
Chemistry is the reason. A basic refractory such as magnesia is destroyed by acidic slag and a silica one is destroyed by basic slag, so the lining is chosen to match what will be run against it. Getting that wrong is the commonest way a furnace lining fails early.
Compound
Aluminium oxide
Industrial alumina — the refined intermediate between bauxite and aluminium metal, and a major ceramic in its own right.
Mineral
Forsterite
The magnesium end of the olivine series — a refractory mineral that makes furnace linings and, in gem quality, peridot.
Mineral
Graphite
Carbon in stacked sheets — soft, slippery, electrically conductive, and chemically identical to diamond.
Material
Mineral wool
in its high-temperature grades, as furnace and pipe insulation to around 1000 °C
Mineral
Olivine
The green magnesium-iron silicate that makes up most of the upper mantle — the most abundant mineral inside the Earth.
Material
Refractory brick
The lining every furnace is built from — and it is chosen to match what will be melted against it, not for how hot it can get.
Compound
Silicon carbide
A synthetic ceramic close to diamond in hardness, and the first commercially successful manufactured abrasive.
Compound
Silicon nitride
The ceramic that tolerates thermal shock — bearings that run without oil, and the one that nearly became an engine.
Material
Technical ceramic
Engineered inorganic non-metallic materials — hard, heat-resistant, chemically inert, and brittle in a way that governs how they are used.
Element
Tungsten
The highest melting point of any metal, which is why lightbulb filaments were made of it and why it is used to drill through everything else.
Each of these uses is established and cited on its own. Whether something counts as an ore, for instance, depends on grade, price and era — and those qualifications are shown alongside it.