Gems

Diamond, ruby, sapphire and emerald: from the absence of color graded D to the red of chromium, the blue of iron and titanium and the green of chromium and vanadium.

Padparadscha, pink and yellow: the same corundum as the blue sapphire, with other trace elements.

From the D-to-Z scale to fancy diamonds: yellow, brown, blue, green, pink and red, and what causes each color.

The same mineral as emerald in other colors: the blue of iron, the pink and red of manganese, gold and colorless.

Crystalline quartz and chalcedony: from the purple of amethyst to the green of nickel in chrysoprase.

Seven garnets, from the red of iron to the green of chromium and vanadium. Some garnets even change color with the light, like alexandrite.

One of the widest color ranges of any gem: from the red of manganese to the blue of iron and the neon of copper in Paraíba tourmaline.

The red of chromium, the purple of iron and chromium, the blue of cobalt and the grayish blue of iron.

Eight transparent gems, from the orange of imperial topaz to the color change of alexandrite and the blue of tanzanite.

Opals, turquoise, lapis lazuli, malachite, jade and moonstone: body colors and plays of light.

Pearls, amber, coral and jet: gems born of living things, colored by organic molecules, layers of nacre and pigments.

The stones of each month in two trade lists: Jewelers of America (US), created in 1912, and the National Association of Goldsmiths (UK). They are trade lists, not official standards.