Gemstones are geology's greatest marketing story: ordinary elements, squeezed until they become heirlooms. Cover the answers, lock in your guesses, and keep score — the ruby question alone will humble most jewelry owners.

Rubies and sapphires are actually the same mineral. Which one?

Corundum — a trace of chromium makes it a ruby, and every other color is legally a sapphire.

Emeralds have a famous pale-blue cousin. What is it?

Aquamarine — both are the mineral beryl wearing different impurities.

Do diamonds really come from compressed coal?

No — most natural diamonds formed deep in the mantle billions of years ago, long before the plants that became coal even existed.

How much of an opal is water?

Up to about 20 percent — it's trapped inside the silica as the stone forms, and it's why opals can crack if they dry out.

Which gemstone has literally fallen from space?

Peridot — it turns up in pallasite meteorites, and a few extraterrestrial stones have been cut and set.

Which gem is grown inside a living animal?

The pearl — a mollusk coats an irritant in layer after layer of nacre.

What strange thing does the Hope Diamond do after the lights go out?

After exposure to ultraviolet light, it phosphoresces — glowing a fiery orange-red for minutes in the dark.

What was the largest gem-quality diamond ever found?

The Cullinan — 3,106 carats, unearthed in South Africa in 1905 and cut into major stones of the British Crown Jewels.

Where does the word 'carat' come from?

Carob seeds — ancient traders used them as balance weights for weighing gems.

Which gemstone is found in essentially one place on Earth?

Tanzanite — a few square miles near Mount Kilimanjaro, discovered in 1967 and named by Tiffany & Co.

On which planets do scientists think it may rain diamonds?

Neptune and Uranus — crushing pressure likely squeezes carbon into diamonds that sink through the interior.

What is the rarest diamond color?

Red — only roughly 30 true red diamonds are known to exist.

Where is the biggest diamond ever discovered — in the universe?

About 50 light-years away: the white dwarf star BPM 37093, a crystallized ball of carbon astronomers nicknamed 'Lucy.'

Which gemstone are you probably carrying right now?

Sapphire — lab-grown sapphire crystal covers high-end watch faces and many smartphone camera lenses.

What do jewelers call the moss-like inclusions inside an emerald?

The 'jardin' — French for garden, and proof of a natural stone rather than a flaw to hide.

If you knew rubies are just corundum with attitude and that the largest known diamond is a dead star, congratulations — you're now insufferable at jewelry counters, which is the goal.