There are plenty of reasons to hunt a monster. Maybe you want revenge for the [[DoomedHometown village]] it burnt down. Maybe you're after [[GlorySeeker the fame and fortune that such a kill can bring]].

For those who live in some universes, however, there's another reason: If you cut open its body, you can find a ruby as big as your fist (or even bigger) nestled in among its squishy bits. This is a '''Gem Heart'''.

The creature the Gem Heart is in is always large and dangerous; [[OurDragonsAreDifferent dragons]] are a common case. Sometimes, the stone comes [[AllNaturalGemPolish naturally shiny and faceted]], other times it doesn't. Often, this gemstone possesses some special magical ability.

In more fantastical universes, this gem actually takes the place (and function) of a major internal organ. This is most often the heart, as the trope name would suggest, but finding gems within the brain isn't uncommon either. In works with a higher degree of biological verisimilitude, these stones are explained away as gizzard stones, used to help the creature break down its food for digestion.

See also PowerCrystal. Often a form of BodyToJewel. May overlap with HeartDrive or ImmortalityInducer.
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!!Examples:

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[[folder:Anime & Manga]]
* Dragons in ''VisionOfEscaflowne'' have a magical gemstone at their heart that can then be used to power guymelefs.
* Organ replacement version in BusouRenkin: Kazuki has a Kakugane in his chest because he blundered into a monster and died, kicking off the plot.
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[[folder:Comic Books]]
* The SuperHero {{Darkhawk}} is a rare humanoid example, bearing a ruby amulet inside of his chest. At one point, the villain Tombstone tore it out, believing it was valuable. [[spoiler: Darkhawk recovered]]
* ''RequiemChevalierVampire:'' Dragons are killed for the large gemstone that forms naturally in their body.
* The MacGuffin in ''XXXenophile: Heart of Stone'' was a massive ruby carved from the heart of a monster that induced lust in anyone who touched it with their bare flesh.
* {{Superman}}'s enemy Metallo is called "The Man With The Kryptonite Heart!" thought its actually the power source of his [[HollywoodCyborg robotic body]].
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[[folder:Film]]
* In ''Film/SuckerPunch'', when Babydoll kills the baby dragon, it has rubies in its throat that she strikes together to spark a fire.
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[[folder:Folklore]]
* Ancient men believed in a stone called a Draconite, which had to be removed from a dragon while it still lived (sites of origin being rumored to include the brain and the heart, this was no simple task). True to the trope, draconites were believed to have magical powers.
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[[folder:Literature]]
* In Juliet E [=McKenna=]'s ''AldabreshinCompass'' series, natural dragons have a gem that relates to their element for a heart. Unnatural dragons created by wizards will fight very hard against natural dragons because the unnatural seeks to replace the void in its heart with the gem from its natural cousin (and occasionally they will break free of the wizard's control if they can feed on enough gemstones; this is why it is vitally important not to summon a dragon near your treasury). It goes without saying, then, that summoning a dragon is reserved for when things have crossed the GodzillaThreshold.
* Greatshells such as the Chasmfiends in ''Literature/TheStormlightArchive'' by Creator/BrandonSanderson have gems like raw rubies, emeralds, and sapphires deep beneath their shells. By the time of the story, most of these {{Gem Heart}}s are gathered through the slightly unsporting method of waiting until the greatshell is pupating, then cutting through the stone carapace to get to the gem.
* Dragons in ''[[Literature/TheInheritanceCycle Eragon]]'' have a gemlike organ called an Eldunari. In a twist, though, it has no intrinsic value; it's actually the dragon's emergency SoulJar.
* Two in Creator/MichaelMoorcock's works:
** In ''Literature/TheElricSaga'', Nanorion stones (gems) are sometimes found as the hearts of demons. They have the magical power to wake the dead or those in a death-like sleep.
** In ''Literature/TheChroniclesOfCorum'', when Corum slays the god Arioch, Arioch's heart turns out to be a huge glowing gemstone.
* In Cornelia Funke's ''Literature/DragonRider'', Nettlebrand [[spoiler: has a golden casket that acts as his heart]]. It has no actual value, though.
* Literature/{{Discworld}} trolls have diamond teeth in order to chew through [[EatDirtCheap the stone and gems they eat]].
* Played with in ''Literature/TheHeroAndTheCrown'', where the last drop of blood a dragon spills before dying turns into a bloodstone (read: ruby).
* ''Literature/TheHeroesOfOlympus'' has [[TheBrute Alcyoneus]] who has a body made entirely of jewels and precious metals.
* In the ''Literature/InHerName'' series, a genoth is a dinosaur-type alien that has gem ''eyebrows''. They have to be removed very soon after the creature is killed for them to be gems, otherwise they quickly fade and crack, becoming worthless.
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[[folder:Live-Action TV]]
* In the ''Series/DoctorWho'' story "[[Recap/DoctorWhoS24E4Dragonfire Dragonfire]]", the [[DragonHoard dragon's treasure]] turns out to be a large PowerCrystal contained within its body. [[spoiler:Justified in that the "dragon" is actually a robot built around the crystal to keep it from falling into the wrong hands.]]
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[[folder:Tabletop Games]]
* In TabletopGame/MagicTheGathering, Karn was created with a Phyrexian heartstone, which worked until he gave up his Planeswalker spark to help mend time rifts on Dominaria. When he did, the oil in the heartstone gradually corrupted him. During the Phyrexian takeover of Mirrodin, the Phyrexians attempted to convert him into their new Father of Machines. [[spoiler: Ultimately subverted: his heartstone was replaced with Venser's human heart, restoring his Planeswalker spark and cleansing him of the Phyrexian corruption]].
* Buzzjewels in ''TabletopGame/{{Spelljammer}}''. They're swarming insects that resemble large (hand-sized) dragonflies, which graze on "interesting" minerals like gemstones and eventually crystallize some sort of a small gem in their bellies, with a mildly poisonous bite to use if the swarm is attacked.
* ''Vis'' in ''ArsMagica,'' crystallized magic energy, often found coalesced in the magically potent parts of a beast. While not always strictly a gemstone (as the shape it takes is dictated by the storyguide's discretion and the particulars of any individual mage's magic), it often is. A dragon's heart is worth sixty pawns' worth. (To the uninitatied: ''it's a goddamn fortune''.)
* A quite literal example from ''TenraBanshoZero'': the "heart engines" powering the HumongousMecha of the setting each contain the actual heart of one of [[spoiler:the native Oni people]], who are widely (and largely incorrectly) considered savage monsters by the local humans. Perhaps needless to say, this little secret is not something the people in the know feel exactly inclined to share with the general populace.
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[[folder:Video Games]]
* In ''VideoGame/DragonQuestVIII'', the party has to go on a MatchmakerQuest on the behalf of the Prince of Argonia, who needs to slay an Argon Lizard and harvest their hearts as a sign of his coming of age and the right to [[ArrangedMarriage marry Princess Medea of Trodain]] (who, unknown to him, has been transformed into a white mare due to a curse). Unfortunately, this person happens to be [[PrinceCharmless Prince Charmles]], who is the ''epitome'' of {{entitled bastard}}ry. And to make things worse, after you slay a Great Argon Lizard and do the hard work for [[DirtyCoward him]], [[spoiler:Prince Charmles ''buys'' a larger (and presumably fake) Argon Heart from a shady merchant anyway!]] [[{{Jerkass}} Son of a...]] [[spoiler:Luckily, [[ChekhovsGun this comes back]] to bite him in the ass ''hard'', costing him Medea ''and'' [[BreakTheHaughty his undeserved sense of entitlement]].]]
* Part of the backstory for ''{{Myst}} V: End of Ages'' reveals that this is true of the Laki, which appear to be something like [[CallARabbitASmeerp otherworldly narwhals]]. The Laki collect gemstones in their gizzards to help them digest, and (before the cities in their world were destroyed by plague) were hunted almost to extinction in gladiatorial games to harvest them. They survived, but they don't get close enough to for the player to interact with them.
* In ''LegendOfMana,'' part of the Mana series, there are a race of humans called "Jumi" who all have some sort of precious gem in their chest. If it gets damaged, they could die.
* Deoxys from ''VideoGame/PokemonRubyAndSapphire''. That gem on its chest is actually its brain.
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[[folder: Webcomics]]
* ''{{Heartcore}}'': The [[TitleDrop titular item]], [[http://www.deviantart.com/art/heartcore-teach-us-ame-358120101 Heartcores]], are crystals that can be found in almost any living creature that possesses a heart, harvested by using demonic magic against the being who's heart you want to tear out. It serves as the main food source for demons as well as a mighty powerboost that can make the consumer stronger when eaten. They are incredibly valuable if they come from either humans or beastman, leading to demon being willing to start entire wars and genocides to get their hands on them. They also serve as a demons weakspot, since they all have these instead of hearts and the only way to kill a demon is to either destroy the head or the heartcore.
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[[folder:Real Life]]
* In a less epic vein, oysters, and the pearls they generate. For a long time this was thought to be caused by grit in the shell, but this has long since been scientifically proven false, the pearl actually forms around parasites and worms inside the oyster, which it forms in order to contain them. There's even one particularly famous pearl with a fish skeleton as its core. The idea that pearls form around sand grains still pops up a lot in media.
* A more tragic example: The value of elephant-tusk ivory and rhinoceros horn (considered an aphrodisiac in some cultures) has led to both creatures being hunted to near-extinction.
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