Medicinal

These are materials used in or as medicine, and the group is unusually varied because the requirements are: some are given to a patient, some are implanted, some emit radiation from outside, and some are there precisely because the body cannot absorb them.

Barium is the clearest illustration. Barium compounds are toxic, and barium sulfate is given by the litre as a contrast medium — because it is so insoluble that essentially none of it enters the body. The dangerous thing about an element is a fact about a compound.

• Element

  Actinium

  as actinium-225 in targeted alpha therapy

• Alloy

  Amalgam

  as dental amalgam, the standard filling material for over a century and still in use where the alternatives are unaffordable

• Mineral

  Baryte

  as the barium meal — insoluble, so it passes through opaque to X-rays and unabsorbed

• Element

  Holmium

  as the active ion in surgical lasers, not as a substance given to a patient

• Element

  Lutetium

  both as a scanner detector material and, as an isotope, a targeted therapy

• Compound

  Salt

  as saline, which is the most administered substance in medicine by volume, and as the iodide carrier that ended endemic goitre

• Element

  Technetium

  as technetium-99m, a diagnostic tracer rather than a treatment

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.