This is a smaller family, and the quickest way to understand it is as the cousin of the sulfides.

The definition: an arsenide is a mineral where the metal is joined to arsenic (written As) — a famously poisonous element. Arsenides often turn up right next to sulfides in the same deposits, which is why they feel like family.

The star minerals

• Nickeline — a source of nickel.
• Cobaltite and skutterudite — historic sources of cobalt.

Fun bit of history: the word "cobalt" comes from kobold, a goblin in German folklore. Miners blamed goblins when this ore poisoned them and refused to smelt nicely — the "curse" was really the arsenic.

The one thing you must remember

Arsenic is toxic. When you roast or smelt these ores, they release arsenic fumes (arsenic oxides) that are dangerous to people and the environment. So the defining challenge of this family is simple: capture those fumes, never let them escape.

This is actually why families are so useful. The moment you hear "arsenide," you instantly know the hazard, before anyone tells you anything else. That's the power of grouping minerals by what they're made of.