Diamond

Chipping them out of cave walls is how most people get their first few, and it is slow work that depends on walking past the right wall. Two things scale better. An Extractinator turns silt, slush and desert fossil into gems as a byproduct of mining you were doing anyway, so haul the junk home instead of leaving it on the floor. Geodes crack open into them often enough that every one you find in the marble caves is worth breaking. If you want a renewable supply rather than a pile, plant a Diamond Gemcorn. A grown gem tree pays back many times the single stone you buried, and unlike a vein it comes back.

A loose gem is mostly a crafting input, and the building materials are the reason to hoard rather than sell. Gemspark blocks glow on their own, which makes them the tidiest way to light a large build without hanging torches everywhere. The stone block version is the subtler option, a speckled wall material you can turn back into loose gems later if you change your mind, though that conversion wants a graveyard to work in. The Rubblemaker will also produce small gem clutter for dressing a cave floor.

• Gem caves are worth marking on your map when you fall into one. Most carry a single type; the rare mixed cave holds every gem except amber.
• This is the only gem with no stained glass version, so a full color set of windows will always be missing a pane.
• Placed in stone it reads pale blue even though the loose gem is white. That is an old sprite nobody went back and recolored, not a second mineral.