This family is also defined by how it formed — and it's the most hands-off one of all, because nature did most of the work before we even arrived.

The definition: as water and wind move sediment around, they wash away the light, common sand (ordinary quartz) and leave behind the heavy, tough grains. Over time those valuable heavy grains pile up and concentrate. We call the result heavy mineral sands, and when it happens in a riverbed for gold, a placer.

What they give us

• Ilmenite and rutile — titanium minerals. Here's a surprise worth remembering: most titanium doesn't become metal — it becomes white pigment (the bright white in paint, plastic, and paper).
• Zircon — used in ceramics, heat-resistant linings, and nuclear work. It almost always travels with the titanium sands.
• Placer gold — pure gold washed out of hard rock and collected in riverbeds. This is the classic gold-panning and Klondike image.

How we separate them

Because the valuable grains differ from one another in weight, magnetism, and electric charge, we sort them physically — gravity, magnets, and static electricity — with little or no chemistry. Compared with smelting, it's cheap and clean.