Cobalt is a hard and valuable, Ferrous transition metal, primarily used to harden Stainless Steels, for turbine engines, and other Aerospace Applications. Cobalt is also a trace Plant Nutrient.

Samarium Cobalt is a stable, high strength, permanent magnet material, that has become the industry standard for Acoustic Speakers.

Refractory transition metals, as a rule, are generally hard, dense, corrosion resistant, and valuable as additives to Stainless Steel alloys.

Refractory transition metals to the left of the Manganese - Rhenium column, are considered to be part of the Tungsten group of metals, and refractory transition metals to the right of the Manganese - Rhenium column, are considered to be part of the Platinum group of metals, as a simple metal naming convention.